Man-in-motion

A player on offense who is moving backwards or parallel to the line of scrimmage just before the snap. In American football, only one offensive player can be in motion at a time, cannot be moving toward the line of scrimmage at the snap, and may not be a player who is on the line of scrimmage. In Canadian football, more than one back can be in motion, and may move in any direction as long as they are behind the line of scrimmage at the snap.