Panther Style
You can strike back at enemies who attack you when you move.
Prerequisite: Wis 13, Combat Reflexes, Improved Unarmed Strike.
Benefit: While using this style, when an opponent makes an attack of opportunity against you for moving through a threatened square, you can spend a swift action to make a retaliatory unarmed strike attack against that opponent. Your attack is resolved after the triggering attack of opportunity.
Source: Ultimate Combat, p. 112