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Defensive Scheme Encyclopedia

A master reference guide to the fronts, coverages, and concepts used by modern NFL defenses.

Base Fronts

A Base Front refers to the initial alignment of the defensive linemen (DL) and linebackers (LB) before the ball is snapped. This alignment dictates how the defense protects the "box" against the run (`A`, `B`, and `C` gaps) and creates rushing lanes to pressure the quarterback.

4-3 Defense

The classic 'even front' consisting of 4 defensive linemen (2 ends, 2 tackles) and 3 linebackers. Each lineman is typically responsible for one gap (one-gap scheme), emphasizing speed and penetration.

Pros
  • Strong pass rush from the front 4 without blitzing
  • Linebackers are free to flow to the ball
  • Good against outside runs
Cons
  • Can be vulnerable to power runs up the middle if tackles are small
  • Requires elite defensive ends

3-4 Defense

An 'odd front' with 3 defensive linemen (1 nose tackle, 2 ends) and 4 linebackers. Linemen often 'two-gap' (control two gaps), eating up blocks to let the 4 linebackers make plays.

Pros
  • Disguised blitzes come from any angle
  • Confusing for Quarterbacks
  • Flexibility in coverage
Cons
  • Requires a massive Nose Tackle to demand double teams
  • Pass rush relies more on scheme/blitzing

3-3-5 Stack

A variation often used against spread offenses, swapping a lineman or linebacker for an extra safety (Nickel). It emphasizes speed and adaptability over size.

Pros
  • Elite speed
  • Great against passing spread offenses
Cons
  • Vulnerable to heavy power run formations

4-2-5 Nickel (Modern Base)

The true 'standard' of the modern NFL. 4 Linemen, 2 Linebackers, and 5 Defensive Backs (adding a slot corner). This combats the frequency of 3-WR offensive sets.

Pros
  • Matches speed with 3 WR sets
  • Retains 4-man pass rush
Cons
  • Lighter box makes it harder to stop the run

Dime Defense

A passing-down specialty featuring 6 defensive backs (4 corners, 2 safeties). It replaces a linebacker with a 'Dimeback' to blanket receivers.

Pros
  • Maximum coverage capability
  • Speed on the field
Cons
  • extremely vulnerable to the run

46 Defense

The legendary 'Bear Front' popularized by the 85 Bears. It places 6 or more defenders on the line of scrimmage to overwhelm the offensive line.

Pros
  • Overwhelming pressure
  • Stuffs the run completely
Cons
  • High risk if the initial rush fails

Who runs what in 2025?

Coverage Shells

A Coverage Shell describes how the defensive backs (Cornerbacks and Safeties) align deep downfield. While the front attacks the line of scrimmage, the shell dictates how the defense protects against deep passes, handles vertical routes, and whether they prioritize "stopping the deep ball" vs "swarming the short game."

Cover 0 (Zero Blitz)

Aggressive man-to-man coverage with NO deep safety help. Everyone else rushes the passer.

Pros
  • Maximum pressure immediately
  • Forces quick throws
Cons
  • High risk: If a defender slips, it's a touchdown
  • No help over the top

Cover 1 (Man Free)

Man-to-man coverage across the board with ONE deep safety patrolling the middle of the field (Single High).

Pros
  • Tight coverage
  • Extra safety can rob routes or blitz
Cons
  • Deep sidelines are vulnerable if corners lose 1-on-1

Cover 2

Zone coverage with TWO deep safeties splitting the field in halves. Corners cover the flat.

Pros
  • Great against short passes and flats
  • Hard to throw deep
Cons
  • Weakness in the 'Turkey Hole' (deep sideline) and middle of the field between safeties

Tampa 2

A variation of Cover 2 where the Middle Linebacker drops deep to cover the middle of the field, effectively creating a 3-deep shell disguised as a 2-deep shell.

Pros
  • Updates Cover 2 to stop vertical tight end threats
  • Keeps everything in front
Cons
  • Demands an elite athletic Middle Linebacker

Cover 3

Zone defense with THREE deep defenders (1 safety + 2 corners) dividing the deep field into thirds. One safety plays in the box (Single High).

Pros
  • Extra defender in the box for run support
  • Balanced pass coverage
Cons
  • Vulnerable to 'Seams' and horizontal flooding

Cover 4 (Quarters)

Zone defense with FOUR deep defenders, each taking a quarter of the field. Safeties read run first, then drop.

Pros
  • Prevents deep passes
  • Safeties can help in run game aggressively
Cons
  • Soft against short/intermediate routes

Advanced Terminology

Zone Blitz

Sending 5+ rushers (blitz) while keeping safe zone coverage principles behind it. A lineman might drop into coverage while a safety blitzes, confusing the QB.

Pros
  • Utter confusion for blockers and QBs
  • Safe against hot reads

Gap Integrity

The concept that every defensive player is responsible for a specific 'gap' between offensive linemen (A, B, C gaps). If one player abandons their gap, the defense fails.

Pros
  • Essential for stopping the run

Simulated Pressure (Sim Pressure)

Showing a heavy blitz look pre-snap, but dropping defenders into coverage while rushing only 4. The goal is to make the QB *think* a blitz is coming.

Pros
  • Forces hot throws into coverage
  • Confuses protection schemes

Wide-9 Technique

A defensive end alignment far outside the offensive tackle/tight end. It creates a massive angle for rushing the QB.

Pros
  • Elite pass rush angles
Cons
  • Leaves huge gaps in the run game inside (B-Gap)