Well, a linebacker is part of the defensive. They will line up about 3 to 5 yards behind the line of scrimmage, which is behind the defensive linemen. That's how they 'back up the line'.
What exactly is a linebacker? Thats an american football position right Yes, a linebacker is a playing position. American and Canadian football use this term. what exactly is thir job on the team and in game?
Linebackers are members of the defensive team, and line up approximately three to five yards (4 m) behind the line of scrimmage, behind the defensive linemen, and therefore ''back up the line.''