Pass interference limits apply only beyond the neutral zone and only if the lawful forward pass in or behind the neutral zone, unaffected by B, crosses the neutral zone. All A and B players are subject to pass interference limitations until the ball is touched or the pass is incomplete. If a receiver is interfered with before he has a chance to catch the ball, it's a penalty. In addition to the basic requirements for pass interference, there is also optional additional interference. This occurs when a defender clearly tries to prevent a forward progress of the ball, even though it may not be completely clear whether he succeeds in doing so. The penalty for this type of interference is a loss of down. For example, a defender tries to tackle a player short of the line but misses and instead hits him in the back. This is illegal contact and can result in a penalty flag being thrown on the play. If this happens near the goal line, the referee will stop the game and issue a free kick to the other team. Otherwise, the play would continue and the player who was tackled could run into the end zone for a touchdown. Similarly, if a defender starts to break up a pass and then pulls his arm away from the body, this is called "self-interference". Again, a loss of down results if this violation occurs within the last three yards of the try line.