An illegal motion penalty is a penalty in Football that is called on the offensive team when a player moves or shifts before the ball is snapped in an illegal way. An illegal motion may include more than one player shifting on the offense at the same time or a player moving forward towards the line of scrimmage without coming to a complete stop prior to the snap. An illegal motion penalty is a 5 yard penalty against the offense.
The major part of this penalty is the forward motion towards the line of scrimmage. If this penalty were not called, wide receivers could run at the line of scrimmage to get a running start against the defense.