Your opponent is attempting to pass your guard by underhooking your legs.

Keep your legs heavy so that he cannot quickly establish his passing posture. Release your grip on the lapel and switch it to under his arm.

Once you have gripped under his arm, pull him into you, keeping his posture broken with your grip and the weight of your legs.

Fall back and pass your opposite leg over his head.

Slide your wrist down to the bend in his arm as your start to figure 4 your legs.

Once you have figure foured your legs, squeeze them tightly as you pull your wrist into your chest. You will have a painful biceps lock on your opponent.