Always Alert (Pathfinder Feat)
From D&D Wiki
Gives the user a 50% chance to apply their Vital Strike damage on attacks of opportunity.
Prerequisites: Vital Strike, Improved Vital Strike, Greater Vital Strike, Mythic Vital Strike.
Bonus: The user gains a 50% chance to apply their Vital Strike damage on attacks of opportunity as well as on the first successful attack of each turn.
Normal: Vital Strike only applies on the first attack of each of your turns.