A strategy on offense in which players will move from their original position to a different position prior to the ball being snapped. A motion play is most often used to attempt to get the defense to show what kind of strategy it will be using on a given play, but it can also be used to adjust the offensive formation to give the team an advantage immediately after the snap. Running backs, wide receivers and tight ends may all go in motion. Motion has to be parallel to the line of scrimmage, or the player has to stop for a second prior to the snap to avoid being called for a penalty.
Motion is the main strategy an offense will use to analyze the opposing defense. By sending a receiver in motion, the offense forces the defense to adjust based on the particular scheme that they are using on that play. This can give the quarterback valuable information about how the defense will react to a play call, and it gives him an opportunity to adjust the play accordingly. The other primary use for motion is to alter the formation just prior to the snap to put players in a better position. For instance, an offense can move a tight end from one side of the formation to the other in order to get an extra blocker before running the ball in that direction.