A member of the officiating crew who is primarily responsible for monitoring the line of scrimmage prior to the snap of the ball and the sideline on which he is stationed while the play develops. A line judge is primarily tasked with calling false starts or offsides before the snap and watches for violations on passing plays once the play develops. The line judge is also responsible for signaling when a player has stepped out of bounds.
The line judge is the officiating position most responsible for all penalties involving the line of scrimmage. Line judges must monitor that players are on the proper side of the line prior to the snap of the ball and that there are no movement violations. They must also make sure that all forward passes are attempted behind the line of scrimmage. As the play continues, the line judge must position himself so he can judge plays that go out of bounds, as well as track any pass attempts on his side of the field. Each team has two line judges, and one is considered the head linesman.