Unbalance Opponent [General]
Prerequisites: Defensive
  Martial Arts, base attack bonus +6.
Benefit: During the character’s action, the character designates an opponent
  no more than one size category larger or smaller than the character. That opponent
  doesn’t get to add his or her Strength modifier
  to attack
  rolls when targeting the character. (If the opponent has a Strength penalty,
  he or she still takes that penalty.)
The opponent’s Strength modifier applies to damage, as usual.
The character can select a new opponent on any action.