This is a defensive formation used in football, typically categorized as a type of prevent defense. It may also refer to "zone" defensive strategy used in passing situations. The former is the most common, and is very similar to a standard prevent defense. The quarter defense involves three defensive linemen on the line of scrimmage, a linebacker positioned behind them, and seven defensive backs positioned throughout the field. The goal of this strategy is to prevent the offense from passing the ball while keeping a linebacker close to prevent the quarterback or a running back from rushing the ball.
The less common use of this phrase is a pass defense in which the field is divided into four zones by four defensive linemen. The advantage of this type of zone coverage is it prevents long plays and provides ample coverage to all areas of the field. It is usually combined with other formations, such as a 4-3 or 3-4 set. This more popular usage of quarter defense gets its name from being next in line in the sequence of defenses named after coins, nickel and dime.