Pelvis Stun (3.5e Monk Fighting Style)
From D&D Wiki
A master of the Pelvis Stun is one who can stun with a blow to the pelvis.
1st-Level Skill Bonus: Tumble.
1st-Level Feat: Stunning Fist.
2nd-Level Feat: Improved Trip.
6th-Level Feat: Master Trip.
6th-Level Bonus Ability: A master of the Pelvis Stun gets +2 to her attack and damage rolls when aiming for the pelvis (and an additional +2 to both if she is using her stunning fist). However, from this point on, the master of the Pelvis Stun can only use her stunning fist when aiming for the pelvis. Because of that, the master of the Pelvis Stun can not use her stunning fist on creatures with no discernible anatomy.