2 Part Technique - If your opponent definitively gains the underhook from Half Guard, utilize the Back Step to save yourself from getting your back taken. Generate enough momentum from your free leg to knock him back flat or into you as you land on the opposite side, i.e. the Reverse Half Guard position. While landing, seek Underhook and Head Control, balancing your weight in between shoulder driving pressure, and basing your hip on the mat (not on his hips). Use your free leg once again to kick yourself free from his guard for the Back Step Pass. If you miss the underhook after the Back Step, use both hands to post for balance if he tries to lift your hips off of the mat. Use your chest to drive into his shoulder if he tries to turn over and pummel back your own underhook for the pass.