What it is

A 3-4 defense uses three defensive linemen and four linebackers.

In a game

The nose tackle plugs the middle, the two ends hold their sides, and the outside linebackers rush the passer from the edges. It is hard for the offense to tell which of the four linebackers will rush, so the defense can disguise where the pressure comes from.

More detail

The 3-4 grew in the 1970s in the pros from an older defense with five linemen. When an outside linebacker rushes the passer, it is not counted as a blitz, because that rush is part of the base alignment. The scheme needs a strong nose tackle who can take on two blockers and outside linebackers who can both rush and cover.

Animated diagram

1. Three linemen, with the nose tackle in the middle, and four linebackers line up. The outside linebackers stand at the edges, close to the line.
2. On a pass the outside linebackers rush from the edges, and the three linemen hold the middle.
3. The offense cannot tell before the snap which linebackers will rush, so the pressure is hard to predict.