Bad idea for him. I know that it used to be understood that men should step up to the plate and do something about an errant jackwagon, but the second he steps in, even to defend the woman in question, she will turn right around and start defending the guy she was just getting smacked by against you. Cops see that scenario on domestic abuse calls all the time. Now from your own perspective you suddenly go from a defense of others situation to a situation where you are now an aggressor in a dispute not involving you and now you get to look at assault and battery charges, all captured on film, while the woman he was going to save is now testifying against you in both a criminal AND civil court cases. Keep in mind they will be very interested in the criminal case against you as proving you were an aggressor with video and testimony so once your convicted, that conviction gets to be used against you in the civil trial when they shake you down for money.