Benefit: Whenever you score a critical hit with a melee attack, you can trip your opponent, in addition to the normal damage dealt by the attack. If your confirmation roll exceeds your opponent’s CMD, you may knock your opponent prone as if from the trip combat maneuver. This does not provoke an attack of opportunity. If you are tripped during your own trip attempt, you can drop your weapon to avoid being tripped.
Special: You can only apply the effects of one of the following feats to a given critical hit: Bull Rush Strike, Disarming Strike, Repositioning Strike, Sundering Strike, or Tripping Strike. You may choose to use this feat after you make your confirmation roll.
Advanced Player’s Guide. Copyright 2010, Paizo Publishing, LLC; Author: Jason Bulmahn.