Vesper Primer+Attacks of Opportunity+Defensive Slice
Sphere: Duelist
When a ranged attack is made against you or a creature within your reach (except for unusually massive ranged weapons and ranged attacks generated by spell effects), you may cut the weapon (or ammunition) out of the air, deflecting the attack so the target takes no damage. As an attack of opportunity, make a melee attack roll at your highest bonus. If the result is greater than the attack roll total of the ranged attack, the attack is deflected. You must be aware of the attack and not flat-footed.
Associated Feat: Cut from the Air.