A penalty called when a player impedes another player's ability to catch a downfield pass prior to the ball's arrival. Pass interference can be called on either the offense or the defense, although it is more commonly called on the defense. On defensive pass interference, the penalty is assessed by awarding the offense a first down at the spot of the foul. On offensive pass interference, the offense is penalized ten yards and must replay the down.
Pass interference can only be called if the player could reasonable have made a play on the ball. Also once a forward pass is tipped or deflected, pass interference is no longer a foul.
Pass interference is most often called when a defensive player makes contact with an offensive player before the pass arrives, and that contact inhibits the offensive player from catching the pass. Examples of this contact can be a defensive player who trips up a wide receiver, grabs the arm of a player so that they cannot catch the ball, or a defender who makes contact with an offensive player without looking for the location of the ball. Offensive pass interference is most often called when an offensive player pushes off on a defender in order to become more open and make it easier to catch the football. Pass interference is a judgment call, and can differ depending on the officiating crew. In the event that both players were making equivalent amounts of contact, it can be termed "incidental contact" and no penalty is called.