Combat Instincts (D20 Modern Feat)
From D&D Wiki
You react instinctively when an opportunity presents itself in combat.
Benefit: If you are not flat-footed when an adjacent opponent’s melee attack roll misses you by more than 5, you may immediately make a single attack at your highest attack bonus as a free action against that opponent. You may use this feat a number of times per round equal to your Dexterity modifier.