This simple self-defense technique is one I highly recommend and teach to New York City Police Officers.  It is a non-lethal but effective defense against a frontal assault.  If attacker grabs your shirt with his right hand, grab his wrist your right hand.  Without any other action, there is no incentive to release his grip so you must also throw a kick with your right leg to his groin or knee.  Remember, as a Ju Jitsu practitioner we never let go of our assailant.  When the attacker releases his grip, you whip his arm around in a circular motion bringing down his head.  At this point you must switch hand positions.  Since the assailants arm is now off to his side in behind, your left hand grabs his right wrist.  Your right hand is placed behind his right elbow and you bend his arm with your left hand.  The right hand then grabs your left wrist forming a figure 4.  Drive the assailant to the ground by pushing up forward and in a circular motion.  From this position you could dislocate his shoulder giving your assailant a good reason not to resist.