You easily block enemy escapes.
Benefit: Whenever an opponent you threaten takes a 5-foot step or uses the withdraw action, that opponent provokes an attack of opportunity from you. If the attack hits, you deal no damage, but the targeted creature is prevented from making the move action that granted a 5-foot step or the withdraw action and does not move.
Pathfinder Roleplaying Game Ultimate Combat. © 2011, Paizo Publishing, LLC; Authors: Jason Bulmahn, Tim Hitchcock, Colin McComb, Rob McCreary, Jason Nelson, Stephen Radney-MacFarland, Sean K Reynolds, Owen K.C. Stephens, and Russ Taylor.