Shield Counter p. 60
As your opponent prepares to make his attack, you bash him with your shield and disrupt his attempt.
As an immediate action, you can attempt a shield bash against an opponent you threaten. The shield bash deals damage as normal. This attack is made with a -2 penalty. If your shield attack hits, your target's next attack automatically misses. You can use this maneuver immediately after an opponent declares an attack, but you must do so before the attack's result has been determined.