You are like the turtle posture, opponent try to take your left collar from under armpit.
Grip his right wrist with your right hand, seize his right arm with armpit, in this case, you should seize inner part rather elbow.
Rolling turn with seize arm, and you hold by "gyaku-kesa".
you should change rolling forward depends on his position or condition.
To prevent leave his right arm by catch your armpit. You hold his move by pull his belt (or pants). When you are upside him, you can enforce opponent by hold his chest.