Defensive Formations: The 4-3 Defense
By J.A. Polk

Since the 4-3 was created in the 1950’s, the variations are limitless. Although, players are lined up in different position, in different schemes; the basic personnel stays the same. The 4-3 defense is a 7 man front, which can drop 8 in to “the box”; using a strong safety or cornerback. Every 4-3 variation will consist of: 2 Defensive Tackles (DT), 2 Defensive Ends (DE), Middle linebacker (Mike), 2 Outside linebackers (Sam and Will), 2 Safeties (FS and SS), and 2 Cornerbacks (WCB, SCB). This article will cover three common variations: Base 4-3, Over 4-3, and the Under 4-3.

Section 1: Base 4-3 Defense

Although schemes vary in different system, historically the primary responsibilities of each position in the Base 4-3 Defense are as follows:


Position

Base 4-3 Responsibilities

Strong Defensive End

Lines up either head up or shaded on the Tight End. At the Snap, the DE will jam the Tight-End, not allowing a clean block in the Sam Linebacker. If it is a running play, the DE is responsible for the Outside or C gap. If the Play is passing in M4M Coverage, the DE will become a primary pass rusher. In zone Blitz scheme this player could be responsible for the Hook/Curl or Flat Areas. 

Strong Defensive Tackle

B Gap Defender; stop the inside runs. Pursue the Quarterback.

Weak Defensive Tackle

A Gap Defender, stop the inside runs. Pursue the Quarterback.

Weak Defensive End

C Gap Defender, Stop or Funnel in Outside runs and cutback lanes. Generally the best pass rusher. Can cover the same zones as the Strong Defensive End.

Middle Linebacker (Mike)

Lines up five yards off the Center; responsible for the A Gap. In cover 2 and 3 zone schemes, the Mike Linebacker will mirror the TE for 5 Yards, After Five Yards the Mike Linebacker will rove the middle of the field. Mike Can be sent on A Gap Blitzes or be included in stunts, generally swapping gap responsibilities with the DT.

Strong Linebacker (Sam)

The Sam Linebacker Sam linebacker is responsible for the strong side c gap. In Cover 2 and 3 zone coverage, the Sam Linebacker will be responsible for the Hook/Curl Zone. In M4M coverage the Sam Linebacker is responsible for the strong side Running Back, or the Tight-End; depending upon schemes. The Sam Linebacker can blitz in both the 2 Deep/ 4 Under Cover 2 Scheme or the 3 Deep/ 3 Under Cover 3 Scheme. In M4M, if the Sam Linebacker’s key stays in to block, the Sam could blitz the quarterback, or spy for the screen and delay route.   

Weak Linebacker (Will)

The Will lines up 5 yard off the LOS, and is a B Gap Defender. In zone coverage, the Will Linebacker will have the same responsibilities as the Sam Linebacker. IN M4M Coverage, the Will linebacker will be responsible for the # 2 Receiver on the weak side. 

Strong Safety

Lines up 12 yards off the LOS. On running plays, the SS plays run support. In Cover 2 zone the free safety is responsible for 1/2 of the deep secondary.  The SS can also cover the flat in the Cover 2 Invert; where the cornerbacks are responsible for the deep secondary. In Cover 3, the SS will be responsible for 1/3 of the deep secondary; the Flats on corner blitzes; and as a blitzing backer in
3 Deep/ 3 Under schemes. In M4M Coverage, the SS will be responsible for the # 2 receiver, or involved in run blitzing schemes. 

Free Safety

The Free Safety generally has the same responsibilities that the Strong Safety has, except there is a greater emphasis on pass coverage than blitzing and run stopping.  

Cornerbacks

Both Cornerbacks have the same responsibility. The Corner is the outermost containment on running plays, if the play-action, they pursuit to the ball, watching for the counter or play-action. In Cover 2 the corner is responsible for the flats, or blitzed in 2 Deep/4 Under. In Cover 3 the corner is responsible for either the deep 1/3 of the field, or the flat areas; can also blitz in 3 Deep/3 Under Schemes. IN M4M Coverage the Cornerback lines up in front of the WR, as the WR pushes out, they re-route the WR inside. After the receiver breaks, the Cornerback will trail, the WR looking for ball delivery. 

Keep in Mind that as offensive alignments change such as: motions or shifts, some position responsibilities will change.

How to Run a 4-3 Football Defense: All about the 4-3 Defense
By: Expertvillage

Section 2: Under 4-3 Defense

The Under 4-3 put the playmakers in position to make those plays. One major advantage is the one-on-one rushing match-ups created on passing downs; while still placing a emphasis on stopping the run. The Basic Responsibilities of the Over 4-3 are as follows, remember that as formations change, through shifts or motions, some player responsibilities will change:


Positions

Under 4-3 Responsibilities

Strong Defensive End

Lines up On the outside shoulder of the Strong Tackle; the DE is a C Gap Defender. Can drop back in zone coverage, generally during blitzing situations.

Strong Defensive Tackle

Shades the Center to the Strong Side, and is the Strong Side A gap defender. Focus on stopping runs and occupying combo blocks. In passing situation, the SDT pursues the Quarterback.

Weak Defensive Tackle

Lines up on the outside shoulder of the Weak side Guard, and is responsible for the Weal side B gap. Focus on stopping runs; In passing situation, the SDT pursues the Quarterback.

Weak Defensive End

Lines up on the outside shoulder of the Weak side Tackle, and is the C Gap defender, and outside containment responsibilities. On running plays is responsible for counters, and cutting off any weak side cutbacks. In passing situation, rush the quarterback.

Middle Linebacker (Mike)

Lines up 3-4 yards deep over the Strong Side B gap. The Mike Linebacker is responsible for shedding blocks and stopping the inside runs, or scraping out on outside runs. The Mike Linebacker can also blitz in zone schemes, and cover the running back in M4M schemes. 

Strong Linebacker (Sam)

Lines up on the outside edge over the Tight End. The Sam Linebacker will never allow the Tight End to make a clean break off the LOS. Can be used in both zone coverage and blitzing schemes. On run plays, the Sam Linebacker must avoid the Tight-End’s reach block, and maintain the outside contain; this should funnel any runs into the formation.

Weak Linebacker (Weak)

Generally the fastest and best pass covering linebacker, the Will linebacker lines up 3-4 yards deep over the Weak side A Gap. The Will Linebacker is responsible for Shooting the A Gap and stopping the inside runs, or scraping out on outside runs.  The Will Linebacker can also blitz in zone schemes, and cover the running back in M4M schemes

Strong Safety

Lines up 12 yards off the LOS. On running plays, the SS plays run support. In Cover 2 zone the free safety is responsible for 1/2 of the deep secondary.  The SS can also cover the flat in the Cover 2 Invert; where the cornerbacks are responsible for the deep secondary. In Cover 3, the SS will be responsible for 1/3 of the deep secondary; the Flats on corner blitzes; and as a blitzing backer in
3 Deep/ 3 Under schemes. In M4M Coverage, the SS will be responsible for the # 2 receiver, or involved in run blitzing schemes.

Free Safety

The Free Safety generally has the same responsibilities that the Strong Safety has, except there is a greater emphasis on pass coverage than blitzing and run stopping

Cornerbacks

Both Cornerbacks have the same responsibility. The Corner is the outermost containment on running plays, if the play-action, they pursuit to the ball, watching for the counter or play-action. In Cover 2 the corner is responsible for the flats, or blitzed in 2 Deep/4 Under. In Cover 3 the corner is responsible for either the deep 1/3 of the field, or the flat areas; can also blitz in 3 Deep/3 Under Schemes. IN M4M Coverage the Cornerback lines up in front of the WR, as the WR pushes out, they re-route the WR inside. After the receiver breaks, the Cornerback will trail, the WR looking for ball delivery. 

Under 4-3 Cover 2 Man Defense explained
By: MightyGaints1

Section 3: Over 4-3 Defense

Here is the Basic Responsibilities in the Over 4-3 Defense:

Positions

Over 4-3 Responsibilities

Strong Defensive End

Lines up on the outside shoulder of the Strong Side Tackle. C Gap Defender on running plays, with Quarterback pursuit and outside containment on passing plays. Can defend the Hook/Curl area in some zone blitzing schemes.  

Strong Defensive Tackle

Lines up on the Strong Side Guard. B Gap Defender on running plays, Quarterback pursuit on passing plays.

Weak Defensive Tackle

Shades the Center to the Weak side of the formation. Is a Weak side A Gap defender on running play, with Quarterback Pursuit on passing plays.

Weak Defensive End

Lines up on the outside shoulder of the Weak Side Tackle, Can either be responsible for the B Gap or outside containment on running play; depending on the Will’s Assignment. Quarterback pursuit, with outside containment in 4- man blitz packages. Can be included within stunts in 5-man blitz packages.   

Middle Linebacker (Mike)

Lines up over the Center, Strong-Side A Gap Defender. Primary role is stop all inside runs, while scraping towards the ball on all outside runs. In Zone Pass Coverage primary area is the Short Middle or Hook/Curl. Can be used in 3 Over/ 3 Under Blitz schemes, and 2 Over/4 Under Blitz schemes. In M4M Coverage, the Mike Linebacker generally covers the Strong-Side Running Back.

Strong Linebacker (Sam)

Lines up On the outside Shoulder of the Tight-End or in a 9 if the Tight-End is not present. Primary Role is Outside Containment, on Running Plays; While scraping towards the Weak Side on Counters Reverses, or weak side sweeps. In Zone Coverage, main responsibility is the Hook/Curl, with Blitzing Options included. In M4M Coverage, Can be responsible for the #2 Receiver, Tight-End or Strong Side Running Back, depending on the scheme.  

Weak Linebacker (Weak)

Lines up outside the Weak Side Tackle. On Running Downs, is Responsible for either the B Gap or Outside Containment; depending on the WDE’s assignment. Will linebacker is responsible for cut back lanes, and will pursue to the ball. In Zone Coverage, is responsible for the Hook/Curl, and is included in blitzing schemes. In M4M Coverage, responsible for the #2 Receiver, Tight-End, or the Weak Side Running Back.       

Strong Safety

Lines up 12 yards off the LOS. On running plays, the SS plays run support. In Cover 2 zone the free safety is responsible for 1/2 of the deep secondary.  The SS can also cover the flat in the Cover 2 Invert; where the cornerbacks are responsible for the deep secondary. In Cover 3, the SS will be responsible for 1/3 of the deep secondary; the Flats on corner blitzes; and as a blitzing backer in
3 Deep/ 3 Under schemes. In M4M Coverage, the SS will be responsible for the # 2 receiver, or involved in run blitzing schemes.

Free Safety

The Free Safety generally has the same responsibilities that the Strong Safety has, except there is a greater emphasis on pass coverage than blitzing and run stopping

Cornerbacks

Both Cornerbacks have the same responsibility. The Corner is the outermost containment on running plays, if the play-action, they pursuit to the ball, watching for the counter or play-action. In Cover 2 the corner is responsible for the flats, or blitzed in 2 Deep/4 Under. In Cover 3 the corner is responsible for either the deep 1/3 of the field, or the flat areas; can also blitz in 3 Deep/3 Under Schemes. IN M4M Coverage the Cornerback lines up in front of the WR, as the WR pushes out, they re-route the WR inside. After the receiver breaks, the Cornerback will trail, the WR looking for ball delivery. 

Stopping the run with a 4-3 (8 men in the box) defense
By MightyGiants1