An overloaded defense in football is a defensive alignment in which most of the defenders will be blitzing the offense when the ball is snapped rather than dropping back into coverage to defend against the passing game. Usually, only three defensive players drop back into pass coverage to cover the deep areas of the field in case of a deep pass. The rest of the players on the defense will be rushing the line of scrimmage to stuff the running back or sack the quarterback.
This defensive strategy is known as 'overload' due to the amount of defensive players rushing the line of scrimmage. Using this strategy, the amount of players on the defense will outnumber the amount of players on the offense at the line of scrimmage, allowing for rushers to get around possible blockers. The offense can counter the overload defense by having extra blockers around the line of scrimmage or passing the ball very quickly after the snap.
When using the overload defense, a team's primary goal is to stuff the line of scrimmage in case of a running play. This works most of the time, but the running back may get free or around the defense. In case of a pass play, the defense will need to get around the blockers very quickly to sack the quarterback before they can pass the ball.
The most common play in the overload defense is called 'engage eight'. This play sends eight defensive players to the line of scrimmage, while three stay in the defensive secondary to prevent deep passes and tackle any receivers in case of a quick, short pass.
Overloaded defenses aren't used too often however, as with advancements in passing offenses and more intelligent quarterbacks who can read the defense more efficiently are becoming more common in the game.