Interference in football is a type of penalty in which a player interferes with an opposing player while trying to complete an action involving the ball, usually when trying to catch the ball. This is known as pass interference and can be initiated by an offensive or defensive player.
Offensive pass interference occurs in one of two ways:
Defensive pass interference occurs when the defender performs an action that inhibits the receiver from catching a pass. This includes bumping, grabbing or pushing the receiver while the ball is still in the air.
When a player is flagged for interference, his team is given a penalty in the form of yard loss. Offensive pass interference results in the offense having to back up 10 yards from the line of scrimmage and replay the down in which the penalty took place. The penalty assessed for defensive pass interference varies based on whether the game is being played at the collegiate or professional level.
At the collegiate level, the offense is given an automatic first down and the ball is moved forward 15 yards. At the professional level (NFL), the ball is placed at the spot of the foul. In other words, if defensive pass interference occurs on a pass 30 yards down the field, the offense is given an automatic first down and begins the next play 30 yards further down the field.