The term "will linebacker" in football is used to describe the weak side linebacker in the standard 4-3 defense. In football, the weak side is defined as the side with the least offensive players to be a threat for the defense, which is typically the side opposite of the tight end. Other similar terms for linebackers are the "mike linebacker and "sam linebacker", which refers to the middle and strong side linebackers.
Linebackers line up behind the defensive linemen, about a few yards behind the line of scrimmage. Like other linebackers, the will linebacker is mostly concerned with stopping runs. However, he also needs to be able to quickly transition to pass coverage due to his position on the weak side. WIll linebackers are typically the most athletic of all the linebackers. They need to be versatile and quick in order to move with the ball carrier and force inside runs. The role that the will linebacker plays is critical to the defense's success and can make or break a game.