From Pathfinder Howl of the Wild, which isn't enabled.

Hunting Snag

FEAT 10

Activity reaction

Trigger A creature within your reach uses a move action or leaves a square during a move action it's using.

Learning from nature's predators has taught you how to keep your prey close. Make a claw or talon unarmed Strike on the triggering creature. If it's a critical hit and the trigger is a move action, disrupt that action. If it hits and the creature left a square adjacent to you, you can Step into that square.

Pathfinder Howl of the WildORC