What it is

A 4-3 defense has four defensive linemen and three linebackers, with four defensive backs behind them.

In a game

Four linemen can stop the run and rush the passer without help, and the three linebackers, the Sam, the Mike and the Will, fill gaps against the run or drop into coverage.

More detail

The 4-3 has been a base defense in the NFL for decades, and coach Tom Landry is often credited with first using it. It comes in variations: the over front shifts the line toward the strong side of the offense, and the under front shifts it toward the weak side. Teams count on the defensive ends to bring most of the pass rush.

Animated diagram

1. Four linemen and three linebackers line up in a row of seven. Four defensive backs are behind them.
2. When the offense runs, the linemen each take a gap and hold the blockers.
3. The linebackers step up and fill the gaps behind them, so the running back meets a defender at the line.