Crab's Claw (3.5e Martial Artist Maneuver)
From D&D Wiki
You crouch low on the ground, simulating the crab. When an enemy strikes you, you lunge out and grasp their leg, slamming them to the ground.
Level: Aggresive 2
Prerequisite: Grapple 4 Ranks
Description: When an enemy succesfully attacks you, you can start a grapple as an immediate action. You also gain a +2 bonus on the grapple.