Unbalancing Strike

Improved Unarmed Strike (PH) , Stunning Fist (PH) (or monk's stunning attack) , WIS 15,

Against a humanoid opponent, you can make an unarmed attack that has a chance of unbalancing your target. If your attack is successful, you deal normal damage and your target must attempt a Reflex saving throw (DC 10 + 1/2 your level + your Wisdom modifier). If the target fails this saving throw, he is thrown off balance for 1 round, losing any Dexterity bonus to AC and giving attackers a +2 bonus on their attack rolls.

Against a humanoid opponent, you can make an unarmed attack that has a chance of unbalancing your target. If your attack is successful, you deal normal damage and your target must attempt a Reflex saving throw (DC 10 + 1/2 your level + your Wisdom modifier). If the target fails this saving throw, he is thrown off balance for 1 round, losing any Dexterity bonus to AC and giving attackers a +2 bonus on their attack rolls.

You can strike a humanoid opponent’s joints to knock your target off balance. This feat is called kuzushi in Rokugan.