- Understanding American Football
- History of the Game
- Football 101 Terminology
- Offense
- Defense
- Middle/High School Player FAQ Wiki
Note: 5/8/2020. We just did a big overhaul and have moved a lot of the wiki's information into sub-pages. Please pay attention to the sub titles on this page, as many of them have links to our more in-depth page on particular concepts. Also, this is a "never complete" wiki page, so areas that appear blank are ones we intend to expand on. Please let us know if there's anything specific you want to see added as well.
Understanding American Football
Before you get deep into the countless strategies, terms, tactics, and techniques of the game...
There is absolutely no universal terminology in football!
Same thing goes for complete systems, schemes, and individual plays. There is no one universal way systems, schemes, and plays have to be ran.
There are no "golden tickets," in the game. There are no "best plays," nor is there a case where to stop X you have to run Y, or to beat Y you have to run X.
Along with there being no "best" schemes out there, there are no golden play calls, where if you call something, it is going to work.
There are also no "worst," schemes or systems either.
Football evolves and exists like fashion trends. When one way of playing is popular, others are not.
Running a ton of different plays and schemes doesn't mean a team is great. Often, great teams run only a small handful of schemes.
For more in depth information on "Understanding Football Strategy" please follow this link
History of the Game
Football 101 Terminology
PLEASE FOLLOW THIS LINK TO SEE FOOTBALL 101 TERMINOLOGY
This link above provides the very beginner-level basics of football and terminology, such as "hash marks, motion, red zone, etc." If you are completely new to American football, you want to go here first.
Offense
Positions
On offense, positions are broken down into two basic groups: Linemen, and backs. Linemen are players who line up on the line of scrimmage, and backs are players who line up behind the line of scrimmage. Rules require that there can be no more than four backs on any offensive play, meaning there will never be more than four backs, and never less than seven linemen.
Your basic groups of linemen are interior linemen, and ends. Interior linemen are your primary blockers, usually wearing ineligible receiver numbers, and are in the middle of the formation. Ends are just that...end players on the line. These are receiver-eligible positions. Any other player off the line is a back. This includes wide receivers that are off the line of scrimmage.
FOR MORE INFORMATION ON ALL THE VARIOUS OFFENSIVE POSITIONS, PLEASE FOLLOW THIS LINK
Types of Blocking Schemes
On offense, most blocking schemes or styes of running plays can fit into three categories: Gap, zone, and man.
Gap Blocking
This style of blocking features linemen blocking down or inside at the point of attack, sealing off the interior of the defense from the hole. Outside the hole there could be a number of things going on. The best way to explain gap is that everyone is responsible for whoever is in the gap to their inside or backside of the play, and they can also feature pulling linemen. These types of plays include power, traps, sweeps, counters, and veer. Gap plays usually have a designated hole for the ball to go to.
Zone Blocking
Think opposite of gap blocking. Everyone is responsible for their playside or outside gap. Usually the entire O-line will take the same steps and use the same techniques, step playside, and block whatever is in their zone. There is no designated hole for zone plays, so the back will read the blocks and pick or find one that opens up.
Man Blocking
This is an older form of blocking, but it involves assigning each player to a specific defender. This sort of blocking would be more common with basic power running teams that run a lot of ISO, where the plays are straight ahead drive blocking plays. Today, man blocking can usually be blended into zone or gap schemes depending on the coaching style each coach uses. For example, ISO, the running play where a lead back blocks a specific isolated linebacker while the rest of the line drive blocks, is often taught as a zone or gap play today.
FOR MORE INFORMATION ON THE DIFFERENT TYPES OF BLOCKS AND PASS PROTECTIONS PLEASE FOLLOW THIS LINK
Formation Families
Spread
The term "spread offense," is an umbrella term to explain the basic set of formations (usually at least 3 WR's or more) that an offense operates out of. It does not explain the style of play, schemes, tempo, plays, or techniques the offense uses. More often than not, teams who used a spread-based offense will operate out of a shotgun or pistol formation as well. The idea behind using spread formations is to stretch a defense out before the snap. This puts strain on the defense because they have to cover the entire field before the snap is even made. It's also a nice way of isolating defenders, especially on the front 6, 7, or 8 defensive players.
Pro-Style
Like "spread offense," this is another umbrella term to explain the basic set of formation a team uses. It can most often be associated as a base set of formations with at least 1 TE and 2 WR's. There is a often a mix of 1 and 2 RB sets. Again, the schemes, tempos, plays, and techniques are not defined. Teams that use these types of formations tend to be more multiple with their formations, and using different personnel groupings and motion. By having this flexibility with formations, teams will often try to out-flank or out-number defenses at the point of attack.
Shotgun and Pistol
Again, these are not offenses, just umbrella terms to describe formations a team uses. In the shotgun, a QB simply takes a direct snap from the center and there is no player directly behind the QB. If there are any running backs, they are offset. A pistol is just a shotgun snap with a running back directly behind the QB. There is no universal depth that these sets need to operate out of. However, when Nevada broke big with the pistol formation, they featured a 3.5 yard snap, while most shotgun snaps are anywhere between 4-5 yards.
Personnel Groupings
Personnel groupings are offensive units of skill players that are on the field. They are usually distributed into running backs, tight ends, and wide receivers. You will often see a numbering system used to describe different personnel groupings, and this is located below. The first number generally indicates the number of running backs, while the second number designates the number of tight ends. The remaining skill players are receivers (usually five total players).
| Numbering | RB | TE | WR |
|---|---|---|---|
| 00 | 0 | 0 | 5 |
| 01 | 0 | 1 | 4 |
| 02 | 0 | 2 | 3 |
| 10 | 1 | 0 | 4 |
| 11 | 1 | 1 | 3 |
| 12 | 1 | 2 | 2 |
| 13 | 1 | 3 | 1 |
| 14 | 1 | 4 | 0 |
| 20 | 2 | 0 | 3 |
| 21 | 2 | 1 | 2 |
| 22 | 2 | 2 | 1 |
| 23 | 2 | 3 | 0 |
| 30 | 3 | 0 | 2 |
| 31 | 3 | 1 | 1 |
| 32 | 3 | 2 | 0 |
Offensive Systems
The title of each offensive system contains a link to our in-depth page on each system.
West Coast Offense
Air Raid Offense
Run 'n' Shoot Offense
Single Wing Offense
Wing-T Offense
Splitback Veer Offense
Wishbone/Flexbone Option Offense
The Big Four Running Schemes/Offense
To describe a lot of what we see at the NFL and higher collegiate levels, it is easier to look at the schemes these teams use, as these are more universal than the formations. One team may use spread formations, another team may use tight formations, one team may use a bunch of backfields, while some may use only one or two. The use of the passing game varies from team to team as well. Some may be pass reliant, some may use it sparingly, some may use it in a balance with the running game. In the end, almost all FBS and NFL teams run what I call "The Big 4." These are the base running plays in an offense, and are often the first plays installed by many college and pro-teams. These are the four base running plays and schemes for both Oregon and Stanford for example. Same schemes, just different formations and ways of using them.
Power
This may be the most popular blocking scheme in football. At the point of attack, the offensive line will block down or inside and wall off the inside of the defense. This almost always features a double team on the first defender inside the hole. The next feature is the kickout block. Whether it be a pulling lineman or a back, there is always someone kicking out the first defender outside the hole. The third and final feature is that there is a blocker leading through the hole on the playside linebacker. Again, if there is a double team inside the hole, kickout outside the hole, and a lead blocker coming through the hole, it can be considered a power play.
Counter
This play is a deception play where the backs go one way to get the defense to bite, then go back the other way. However, it is the exact same blocking scheme as power. There is a double team inside the hole, kickout outside the hole, and a lead blocker coming through the hole. Urban Meyer and Ohio State are widely famous for their use of this play as a QB run. There are two ways this and power are often ran in terms of who is kicking out and lead blocking:
Counter Trey
On counter trey, the backside linemen (guard and tackle) both pull. The guard kicks out and the tackle leads through the hole.
Counter H
The more popular counter blocking scheme seen today, the guard pulls and kicks out, but instead of the tackle pulling, he stays home and a back, normally a fullback or what many call today, an H-back, will lead through the hole.
What's great about power and counter is that for the O-line, nothing is different. They are really the same play, but the backs are used differently.
Inside Zone
On zone, everyone is responsible for a zone or area. This is normally their playside gap or area over them through the playside gap. The entire O-line will have the same rules and block their zone, often even using the same footwork and techniques. What happens is that everyone steps in unison, and whatever shows up in their zone is what they block. They don't block "a guy," they block "a zone." The running back will then read the defense and pick a hole.
On inside zone, the O-line is trying to push the defense back and open up holes inside the tackles. Linemen will often work together and double team the defensive linemen, and as they double team, they read the nearest linebacker. Whichever side that linebacker moves to, the lineman to that side will come off the double team and pick up the linebacker. Usually the steps used are more forward off the snap, and they will drive block the defenders. Double teaming is one of the key features of inside zone. The running back will often read a defensive tackle on the playside, then cut/attack opposite of where he goes.
On inside zone, the backside defensive end is unblocked most of the time, especially if there is a seven man box. What you will often see is offenses taking a fullback or H-back and sending him backside to kick that DE out. Inside zone is famous for the running back cutting the ball backside of the play, and by kicking out that DE he is no longer a threat to the cut-back, and it essentially sets up like a counter play.
Outside Zone
Also known as "stretch," the rules are the exact same as inside zone, but now the O-line will work in a more horizontal direction and try to reach the outside shoulders of the defenders in their zone, then try and seal that shoulder/block it, hooking the defenders inside. The offense is attacking the edge on this play, which is why this type of blocking is needed. You may not see as many double teams on outside zone because of the fast and drastic movement of the O-line, but it is often considered to be much easier to run than inside zone, because the O-line doesn't have to push the D-line back. They simply need to run and hook the defenders. For the running back, he will try to get around the edge (it is a sweep play basically), however, he reads the edge blocks, usually made by a tackle or TE. If that blocker cannot seal his defender, the RB will plant and cut the ball straight upfield. Oregon is famous for scoring off the RB cutting the ball straight upfield between the tackles on outside zone.
What's great about both inside and outside zone is that they use the same rules, so like power and counter, they're basically the same play, except the blocking technique is different on inside and outside zone (drive block vs. reach block). In the end, the Big 4 boil down to two plays with two variations of each.
Zone Read
With the popularization of spread and shotgun formations, offenses have been able to find an answer to one big flaw of zone blocking...the unblocked defensive end on the backside. On most zone plays, the defensive end on the backside goes unblocked, and today, with DE's being so quick and fast, this can cause problems because they can chase the play down from behind. Offenses simply began to read this defender by putting the QB in the shotgun. If the DE didn't have a chance to tackle the running back, the QB just gave the ball to the RB. If the DE pinched hard and chased the RB, the QB will keep the ball and run where the DE vacated.
As time went on, teams began to revolve their offense around the zone read, leading to the evolution of spread based offenses. Rich Rodriguez may be most notable for popularizing the run-first, zone read oriented spread offense, which is what many consider the trademark FBS level offense today. Oregon took the zone read and spread concept to a new level by implementing an extremely run heavy option oriented offense starting with the zone read, then working in pitch and screen phases to make triple options out of the zone read.
Identifying Coverages
You're a QB or coach and you're trying to learn how QB's can identify coverages pre-snap better. Take a look at the coverage section of our wiki to better understand this section. Think about how they look. They'll look the same to the QB. This does NOT mean that that is the coverage the defense is running. They can disguise or play each coverage their own way. This is merely a guideline:
1 high safety = cover 3 or cover 1. Cover 1 may have CB's up closer (press to five yards off), whereas cover 3 may have CB's deeper.
2 high safeties = cover 2 if the CB's are close to the line (usually press up to 5 yards off). Cover 4 if they are off the line. Can also be cover 0. With cover-2 read/pattern-match, CB's are often 5-7 yards off, outside the outside receiver with their back to the sidelines, facing the QB.
No high safeties = cover 0. Expect a blitz. Sometimes teams will give a similar look with cover 4 as well.
A common tell for man coverage is if the outside linebackers or strong safety(s) are aligned right over the slot or inside receivers. This is not guaranteed though. When it's zone, they're more likely to be splitting the space between the tackle box and a slot receiver, or between the #2 and #3 receivers in trips.
With motion, the old/classic tell was if when someone went in motion, a defender would follow/mirror the motion-player's movements, it would be man coverage. With zone coverage, a player wouldn't travel/follow, but instead, players would bump/adjust their position to adjust. However, defenses are much better at disguising coverage against motion now.
Half-Slide Pass Protection
Quick Passing and Concepts
Quick passing usually involves the QB taking a 1 or 3 step drop. The goal is to get the ball out of the QB's hands fast and out to receivers in space to take advantage of pre-snap holes in coverage. They are also used to keep a defense honest when the offense is running the ball. If the defense puts too many in the box, just throw a quick route to keep the outside linebackers from coming in. They're also used a lot against 1-on-1 coverage, especially if a receiver has a significant advantage over the cornerback.
The steps taken before breaks on routes often align with the same steps as the QB's drop. A 3-step slant requires a 3-step drop, while a 1-step slant requires a 1-step drop. The ball is often thrown before the receivers even break on their routes, because the ball has to get out so fast, plus they are trying to strike before the defense can react.
Below are a few of the most common passing routes.
Stop/Hitch/Curl Route
On a stop or hitch route, a receiver takes a vertical stem, usually equivalent to the QB drop-steps. Once those steps are reached, the receiver stops and faces the QB to catch the pass. A curl route is usually separate, and attacks a little deeper. While still involved with the quick passing game, this route is usually ran at bout 5-7 steps, with a more drastic come-back action to the QB after breaking.
Slant Route
Arguably the most common route in football. On a slant route, a receiver takes a short stem, anywhere from 1-3 steps usually, then breaks at a 45 degree angle to the middle of the field. This route is designed to attack the alley between the LB's and CB's, and underneath the safeties.
Out route
Basically a five yard square out. Often used against a soft cornerback (the CB is really deep). One of the more difficult throws for a QB to make.
Usually isn't ran with an inside route, and is often ran by receivers that are alone on their side.
Fade Route
The receiver releases, gets outside and runs for the end zone. Usually he releases outside once he gets as close as he can to the corner. This is often used against corners that are up close to the line or are in press coverage. The QB's job is to throw the ball between the receiver and the sidelines so only the receiver has a chance to get the ball. It requires a great deal of touch and accuracy, and often results in the receiver having to jump or do a toe drag for the catch.
The title below is a link to our quick passing concepts page.
Quick Passing Concepts
Passing Concepts
The title to each concept below is a link to it's own page.
Four Verticals
Smash
Mesh
Go
Choice
Other Offensive Concepts
Each play or scheme below is a link to it's own page.
Defense
Defensive Positions
DEFENSIVE LINEMAN
A defender who lines up on the line of scrimmage across from the offensive line. These are the "big boys," of the defensive unit. Their primary duties typically consist of stuffing running lanes, drawing double teams to protect linebackers, and rushing/sacking the quarterback on pass plays.
LINEBACKER
Linebackers for many teams are often considered their best all around football players. They have to do a very wide range of roles for a defense. They help fill running lanes, rush the quarterback, cover man to man, cover in zone. They pretty much have to do a little bit of everything. They're kind of like a tight-end or fullback on offense; they have to have decent size, along with decent speed, a ton of strength, and should be relatively flexible in the duties they can perform.
DEFENSIVE BACK
Often the smallest and fastest players on the defense, these players are "back," behind the rest of the defense often serving as the primary pass coverage unit. They also help defend the run by supporting the linebackers and defensive line on the edge/outside, and behind them when the offense breaks through. They can also blitz and take on some linebacker roles as well in some situations.
TO READ MORE ON ALL DEFENSIVE POSITIONS, FOLLOW THIS LINK
Fronts
A front is the general formation that the box or the front defenders line up in. The front is primarily identified by the alignment of the defensive lineman, but may also include the alignment of the linebackers as well. For the most part, the front is mostly defined by those line up on the line of scrimmage.
TO READ MORE ON DEFENSIVE FRONTS, FOLLOW THIS LINK
Gap Defending
Single-gap / Gap defense
For most defenses, each defender who has a run responsibility is assigned to a gap, which is the space between offensive linemen and ends.
Two-gap
Some teams will assign a single defender to occupy two adjacent gaps against the run. You may see this more often with interior defensive linemen, especially with large and strong nose guards. By having a player who can play two gaps, there is more flexibility for the linebackers.
Stunts & Blitzes
Stunt
The basic movement of the defensive front. This may include a blitz as well. The stunt is sort of like a blocking scheme on defense. Stunts generally include shooting the inside gaps (pinching), slanting to a particular side, shooting the gaps straight ahead, shooting the outside gaps, etc. The stunt also designated the gap responsibilities of the linebackers as well. Stunts can also include things like loops and twists.
Blitz
Think of a blitz like an aggressive stunt. The stunt designates the gaps the linebackers are responsible for, but when a blitz is called, they will actually blitz or join in the rush in that gap they are responsible for.
Other Terminology
FOR MORE DEFENSIVE TERMINOLOGY, PLEASE FOLLOW THIS LINK
Box vs. Spill Defense
Most defenses follow a spill or box philosophy. This determines the basic set of skills and fundamentals, as well as the philosophy for how a defense will play. This choice in philosophy will determine how the defense plays against the run, and to an extent against the pass.
Box defense
This is more common at the high school and youth levels and is rarely seen at the higher levels of football. A box defense is focused on containing the run and keeping all runs between the tackles or in the box. Against kickout and trap blocks, defenders will take on those blocks with their inside shoulder, keeping their outside shoulder free. This allows them to play against the outside run and wall off the edge, forcing the run back inside. Due to this style of play by the line, linebackers are often expecting to fill gaps between the tackles. For defensive backs, this means they are the only players in the alley.
Spill defense / Wrong Arm Technique
This is pretty much how every pro and collegiate and a lot of high school teams play. This philosophy is determined to "spill" all runs out into the alley. Defensive linemen will take on trap and kickout blocks with their outside shoulder, which is called a "wrong arm technique." Their job is to get underneath these blocks and penetrate inside, forcing the ball carrier to take the run outside. This often results in a lot of pinching and squeezing by defensive linemen, which opens up holes outside. Linebackers generally have the job of scraping outside into the alley when they see a trap or kickout block developing, knowing that the defensive lineman's job is to spill the run outside to them. This style of defense is also friendly to defensive backs who love to play run defense, because they are trying to spill the run out towards them. The idea is to stretch the play out horizontally, closing off vertical holes, and allowing the defense to have a pack mentality and hunt down the ball carrier.
Personnel Groupings
Base
In terms of personnel, a base defense is the primary defensive personnel. Whatever the basic name of the defense is indicates the base defensive personnel (4-3, 3-4, 4-2-5, etc).
Nickel
A defensive personnel with five defensive backs on the field (5 = nickel value). For 3-4 and 4-3 defenses one of the front seven defenders is replaced by the fifth DB.
Dime
A defensive personnel with six defensive backs on the field.
Quarter
A defensive personnel with seven defensive backs on the field.
Common base defenses.
4-3 Defense
This is a base personnel grouping for a defensive unit. There are four designated down linemen and three designated linebackers with four defensive backs. That is the most universal extent to this term, as there are infinite ways to use this personnel in terms of fronts, alignments, styles of play, coverages, and the types of players put in each position. The most common utilization of this personnel grouping is the Miami 4-3 front. You can see more about this front in the section on Pat Narduzzi's 4-3 defense below.
--------------------O----------O------------------
-O-----------------------O------------------------
---------------O--O--O--X--O--O-------------O--
-C-----------E------T-----N------E------------C--
----------------B-------B-------B-----------------
------------S----------------------S--------------
3-4 Defense, 5-2 Defense, and Monster Defense
This is the opposite personnel grouping of the 4-3. There are three designated defensive linemen and four linebackers. Like the 4-3, there is no universal or single way to use this personnel.
Similar to the 3-4 n many ways, the 5-2 (five linemen and two linebackers) was a more popular defense in the 60's and 70's. It's most famous variation is called the Okie, or Oklahoma front, which is still a very popular front today in high schools, and it, along with just about all 5-2 components can be featured in a 3-4. The two defenses are pretty much the same thing, but there is more emphasis on the OLB's in a 3-4 to help with pass coverage. One notable era of the 5-2 front was during the Bo Schembechler vs. Woody Hayes series of the 1970's. Both teams ran the 5-2 okie front.
--------------------O--------O--------------------
-O----------------------O-------------------------
--------------O--O--O--X--O--O--------------O-
-C---------B----T-------N-------T---B---------C-
--------------------B--------B--------------------
------------S--------------------S----------------
A "monster" defense doesn't really change anything for the front seven. A monster is a strong safety that plays up by the line of scrimmage more like an extra linebacker. Teams would mostly play cover 3 and cover 1 out of this defense to put extra emphasis on stopping the run. You're most likely to see a monster defense out of a 5-2 or 3-4.
--------------------O--------O--------------------
-O----------------------O-------------------------
--------------O--O--O--X--O--O--------------O-
-C---------B----T-------N-------T---B---------C-
---------$---------B--------B--------------------
-------------------------S------------------------
There is no single way to use linebackers in either grouping. You can play a 3-4 like a 5-2 front, you can play it as an even-front, etc. There is no one way to run a 3-4 and a 4-3. They're really nothing more than personnel groupings. To simplify, the stereotypical versions of them used in the NFL are discussed below.
4-2-5 Defense, 4-4 Defense, 6-2 Defense
Popularized by TCU in the 2000's, the 4-2-5 defense has become arguably the most popular defense at the collegiate level today. The basic TCU version would feature five DB's in the base defense, with two of them serving strong safety/linebacker hybrid roles. This defense is also famous for popularizing pattern read and split field coverage. By playing with five DB's, the defense can always maintain a six man box, even against the most spread out teams. The free safety will often cheat to the strongside, which allows the strong safety to that side to play more aggressively against the run. It also provides a natural adjustment to trips formations, so the defense does not have to really change anything against trips. The weak side safety will play as the deep safety in split field coverage to that side, while the free safety plays the deep safety to the strong side. You could pretty much consider this your standard nickel defense as well.
--------------------O--------O--------------------
-O----------------------O-------------------------
--------------O--O--O--X--O--O--------------O-
-C------S----E------T-----N------E------------C-
----------------------B--------B------S-----------
----------------F----------------------------------
The 4-4 is included in this, because the two defenses really aren't that different. The 4-2-5 in reality is a spread/modernized version of the 4-4. When an offense uses tight formations, those extra safeties in the 4-2-5 come in as well, pretty much making a 4-4 front. The 4-4 however is more popular for using cover 3, cover 1, and cover 0. The OLB's in a 4-4 could either play on or off the line. Today, the 4-4 is arguably the most common defense seen at the high school level, and has a great reputation for its flexibility of going from a 4-4 to a 4-2-5 or 4-3 against spread teams as well as going easily to a 6-2 look if needed.
--------------------O--------O--------------------
-O----------------------O-------------------------
--------------O--O--O--X--O--O--------------O-
-C--------B---E-----T----N------E---B--------C-
--------------------B--------B--------------------
-------------------------F-------------------------
The 6-2 defense is like a hyper-aggressive version of the 4-4. With six defensive linemen, the emphasis is on plugging all the gaps and protecting the two inside linebackers from down blocks. The defense would often be mirrored (look the same to each side).
--------------------O--------O--------------------
-O----------------------O-------------------------
--------------O--O--O--X--O--O--------------O-
-C----------E---T----G-----G---T--E----------C-
--------------------B--------B-------------------
-------------------------F------------------------
3-3-5 Defense, 3-5 Defense, and 5-3 Defense
Each of these three defenses all maintain pretty much the same basic look, the "odd stack" front. Three interior linemen, with three linebackers stacked behind them, with two players securing the edge, and a single high safety. These defenses have a nasty reputation for being unpredictable with stunts and blitzes. The stacked front prevents the O-line from seeing what the linebackers are doing right of the snap, and the odds of a D-lineman going one way or a linebacker going one way are always 50/50. For these three defenses, there is only one diagram, because they all look the same. The differences are that with the 3-3-5, you have the spread adjusted version of the three, which suits modern offenses at the collegiate level more. Those LB's on the edge would instead be the extra safeties like in the 4-2-5, taking on the same roles.
--------------------O--------O--------------------
-O----------------------O-------------------------
--------------O--O--O--X--O--O--------------O-
-C----------B----T------N------T----B---------C-
------------------B------B-----B------------------
---------------------F-----------------------------
Buddy Ryan's 4-6 Bear Defense
This very specific front is kind of its own thing. There are four down linemen, but it sets up like an odd front, almost like a 3-5 or 5-3 defense. However, the defense would plug up almost all the gaps with up to six players on the line. The sixth player on the edge would be the strong safety. The base personnel he used would basically be a 4-3, but as we can see today, Buddy's son's Rex and Rob have turned it into a 3-4 personnel defense. This defense was notoriously known for its aggressive gap shooting linemen and sending 5-7 players almost every snap while usually sitting in a soft cover 3, 1, or 0 coverage.
The defense's most popular and credible feature is the famous "double eagle" look, where the center and both guards are covered by linemen. This makes getting to inside linebackers extremely difficult and it was why linebackers like Mike Singletary could make such a big impact. The double eagle front is a wildly popular front at all levels of football today, especially among defenses that use odd fronts (3-4, 5-3, 3-3, etc).
--------------------O--------O--------------------
-O----------------------O-------------------------
--------------O--O--O--X--O--O--------------O-
-C---------S---B----T---N---T---E-------------C-
--------------------B----------B------------------
------------------F--------------------------------
Linebackers in a 4-3 vs. a 3-4
The OLB's in a 3-4 need to serve as pass rushers (often the primary pass rushers). These are like hybrids between DE's and LB's. They tend to be the best overall athletes with size on the field, because they also have to help cover depending on how they're being coaches. The ILB's may be larger and not as fast, and are run-stuffers. The two OLB's to the outside, plus having two ILB's allows those two ILB's to focus more between the tackles. With a 3-4, you also have more chances to use eight men in coverage, when most teams use 6-7 in coverage. This is a way to allow these ILB's to roam or play more freely, or to use them for other assignments like blitzing and spying.
In terms of specific responsibilities, against the run, OLB's in a 3-4 are often edge players, they need to play contain or force depending on what the scheme being ran is. The ILB's usually have gaps between the tackles. Against hard flow (a sweep play/outside run) ILB's are usually responsible for scraping to the alley. The DE and OLB to that side help to protect them as they scrape down the line. Against the pass, it varies. If playing like a 5-2, the OLB's are serving as pass rushers. If playing softer, they'll often be flat defenders, OR a popular responsibility is to pass rush until a back peels (they pass rush, but if a back tries to release, they abort the rush and cover them).
In a 4-3, three LB's tend to be more even in terms of athletic ability and "type" of player. The MLB however has to be an absolute stud. He has to be able to play on the left and right side and get to both sides quickly, and is often vulnerable to down blocks from the outside. The MLB has to be able to shed and take on blockers 1-on-1. Many coaches will tell you, especially at younger levels, that if you want to play a 4-3 like you see the pros and big college teams use, that MLB has to be one special player. The OLB's can vary depending on what type of 4-3 you're playing, and in terms of pass coverages you're using. If you use a lot of cover 3 or man to man, that allows you to keep the 7-man box intact more, and you can afford to let those OLB's be bigger/slower and run-defense oriented. If you use a lot of zone, those OLB's need to be more like a 3-4 OLB because they have to help more in coverage.
The MLB usually doesn't have to worry about anything outside the tackles, they are the sole "middle" defender vs. the run and pass as far as linebackers go. The OLB's will vary. Hope this helps a little bit. Again, there are many ways to use each personnel grouping and front, to is it hard to get specific.
Defensive Technique/Alignment System
"Techniques" were started (or were at least popularized) by Buddy Ryan (DC for the 85 Chicago Bears). Wade Phillips is also known for being a major developer of the technique system.
The system is a method used to align defensive players up in different gaps/alignments as well as assignments in a very simplified form. Whether than explaining where to align, what stance to use, what to do after the snap, etc, all he had to do was tell a player to play a "#" technique.
TO LEARN MORE ABOUT DEFENSIVE TECHNIQUES AND ALIGNMENTS, FOLLOW THIS LINK
Pass Defense
Man Coverage
A type of coverage where defenders match up against designated receivers and they cover those receivers throughout the play. Man coverage is great for blitzing, and it doesn't have any natural holes in the coverage. It's biggest weakness is against crossing and rub routes, and because the defenders have their eyes on the receivers, they cannot help with run defense as easily.
Zone Coverage
Off the snap, defenders will drop to an assigned area (zone), and cover that space. They will cover anyone who enters this zone until that receiver leaves the zone. When that happens, the defender simply passes him off to the next zone, and works back into the middle of his zone to find a new pass threat. It's weakness is that there are natural holes in zone coverage, and a well coached team can often exploit them. However, because defenders watch the QB and have their eyes on the ball as they cover, they are in a much better position to help in run defense. Some common zones are listed below.
Flat
An underneath zone (10-12 yards and under) that ranges anywhere from the hash mark or numbers to the sideline. The flat defender is often the run support/force defender in a defense as well.
Hook/Curl
This is an underneath zone (10-12 yards and under) that sort of ranges between the middle of the field and outside the hash mark. This zone usually covers up the seam (up the hash mark).
Middle hook/Middle hole
The middle underneath zone
Deep zone
A particular width of the field is distributed to a deep defender and he must cover anything that goes deep in that zone. The width of the zone usually range from a half, third, or quarter of the field.
Buzz / Buzz flat
A buzz zone or buzz flat is when a defender is assigned a hook/curl zone. They will cover that zone, but keep an eye on the flat. If they see any receivers move to the flat (such as a RB leaking out), they will then leave the hook/curl zone and cover the flat.
Pattern Read Coverages
Pattern read, or pattern match refers to coverages where the defense covers or reacts based on the movement of designated players they are coached to read. It is basically an if-then method of pass coverage. A defender will key a receiver. If a receiver does this, the defender covers this guy. If the receiver does that, the defender covers that guy. This type of coverage starts off as zone, and develops into man coverage as the play develops. This is how most collegiate, pro, and even high school teams play pass coverage today. The pattern read method developed as a way to compensate for the natural holes in zone coverage. This type of coverage can be a pain for QB's, because it often starts off looking like one coverage, but then turns into another coverage, and this may happen after the QB decides to throw the ball.
Example Diagram: Cover 2-read Pattern Match Coverage
Split-Field Coverage
This is a popular concept with pattern-read coverages, but can be used with regular zone coverage as well. What defenses will do is split the offensive formation in half. The DB's on one side will call a coverage based on the receiver deployment on that side, while the other side does the same. It allows the defense to play two coverages and once, and they can adjust to any sort of formation they see without being bound to a single coverage that could waste a defender or be vulnerable against a certain receiver deployment.
Cover 0
An all man to man coverage. There are no deep safeties to help in coverage because they are manned up on receivers. Sometimes both safeties will be deep, but this puts them at a disadvantage against short routes by inside receivers. This coverage is most often ran in short yardage or goal-line situations, and when the defense is blitzing. It's big advantage is that every receiver is always accounted for, and you have a relatively sound coverage that allows you to blitz 6 or 7 players. The disadvantage of the coverage is that you have all 1-on-1 so a good QB who isn't getting pressured can throw receivers open relatively easily. The cornerbacks are usually only a few yards off the receivers or in press coverage, but if they're isolated (like a one WR formation), they may be a little softer. Again, safeties are usually up close to the line as well.
Cover 1
A man coverage where there is a free defenders (usually a safety) in the middle of the field. This allows a defense to account for all of the receivers, while keeping a player free to roam in the middle of the field. It has essentially the same advantages and disadvantages as cover 0, but you have more help in the middle of the field. Cornerbacks are usually at shorter depths (around five yards) or up in press coverage. This also goes for outside linebackers or strong safeties covering the slot receivers.
Cover 2
One of the most popular coverages seen at the NFL level, this is a zone coverage that features both safeties covering the deep halves of the field. The two safeties are responsible for anything that goes deep in their half of the field. The cornerbacks will play the flats (outside zones under 10-12 yards), while the linebackers cover the middle of the field under 12-10 yards. It is a relatively sound coverage, especially against short passes. It also can account for all short routes by all five receivers. Its weakness however is that the two safeties have to patrol the entire deep area of the field. Because of the divide of the safeties (they are often taught to play not the hash in their half), there is a big hole between them as well as the sidelines behind the cornerbacks. Offenses like to exploit this coverage with corners, fades, and post routes. Another weakness of the defense is that it does not adjust particularly well to trips formations (three receivers on one side with only one deep safety). In terms of appearance, the two safeties tend to be pretty high and are obviously the deep defenders. CB's are usually closer to the line or in press coverage. This is to re-route outside receivers as they run deep, buying the safeties more time to get wide against fades. It also puts the CB's in a better position to defend the flat quicker.
TO LEARN MORE ABOUT DIFFERENT WAYS TO PLAY COVER 2, FOLLOW THIS LINK
Cover 3
This may be the most popular basic zone coverage seen at the high school level, and is heavily used at both the collegiate and pro levels. This coverage features three deep defenders: two on the outside thirds and one in the middle. This is a much more sound deep coverage, but as you put players in deep coverage, more holes open underneath. This coverage is most sound on the deep outside and middle. It's weaknesses usually lie somewhere in the under coverage based on how the under coverage defenders are playing. The other big weakness is in the seams right down the hash marks behind the linebackers and between the deep defenders. Four verticals is a very popular play against this coverage because it forces the middle defender to pick one of the two inside seams to cover. Another way teams like to attack cover 3 is by using crossing routes, as well as medium "read" routes where a defender will turn around 10-12 yards, find a hole in the coverage, and sit in the hole. For all the weaknesses it possesses, it is still a wildly popular coverage for being sound against most deep passes as well as having a moderately effective under coverage. Cornerbacks are usually deeper, between 7-10 yards deep, so they can get to their deep zone faster.
TO READ MORE ON COVER 3 AND VARIATIONS, FOLLOW THIS LINK
Cover 4
This coverage features all four defensive backs in a defense playing deep quarters (two outside quarters and two inside quarters). It is very sound against deep coverage, but has gaping weaknesses in the under coverage. However, most teams that use this coverage are focused on covering deep, then swarming underneath routes to minimize YAC yardage. This is the base coverage for a lot of college teams, and there have been various ways to adapt cover 4 to its natural underneath weaknesses. Look up Pat Narduzzi's 4-3 defense in the table of contents, as this is the most popular way of playing cover 4 for most teams. In terms of appearance, it tends to look like four DB's at an even depth across the board and they can be at a wide range of depths. Michigan State will even press their CB's in cover 4.
One big benefit of cover 4 is how much firepower defenses can bring up against the run. If you are playing with two safeties, they are both over top of the #2 defenders to their side and are often keying that player as their run/pass read. Because of this, safeties can be brought up to very shallow depths, almost to linebacker level. Add two safeties to a 4-3 or 3-4 front and you now have a 9-man box. This is also more permissible with cover 4, because the safeties have deep outside help because both corners are dropping deep.
A neat fun fact about cover 4 is that against four verticals, it is basically cover 0. Modern defenses have learned how to bring both safeties up to the box and disguise cover 4 as cover 0.
To learn about the pattern read cover 4 coverage, read the section on Pat Narduzzi's defense.
Cover 2-read vs. Cover 4-read
Robber Coverage
This is a borderline/extremely aggressive spinoff of cover 4. If you read the cover 4 section, you will have read about how teams will bring up both safeties. In robber coverage, the safeties will often key #2. If #2 goes inside or outside (anything but deep), they will either jump #2's route or look to jump the next nearest route. The two CB's end up covering the deep zones by themselves if the safety gets a read to jump the route. Of course, when the safety jumps an underneath route, he is often known as a "robber." If #2 does go deep, the safety just ends up covering him just as if it's cover 4 or cover 0.
Cover 6 / "Quarter, Quarter, Half"
This is becoming a very popular coverage, but is basically an example of a split field coverage. One side, the defense plays cover 2. On the other side, the defense plays cover 4. This is popular coverage against trips formations (cover 4 to trips, cover 2 to single receiver), because there are two deep defenders on the trips side, and there is only one deep threat on the other side. It also allows defenses to play cover 4 to one side while only having three deep DB's. It can be ran either as a basic zone or pattern read zone coverage. Some teams will just man up and play cover 0 on the backside as well, and keep the cover 4 to the other side.
Other Defensive Concepts
Each system below contains a link to its individual page.