How far do you get involved if witness to a lopsided fight?

How far do you get involved if any? You are walking back in a parking lot to get back to your car, from an adjacent parking garage some skinny geeky kid comes tearing out of there as if the devil was after him and close on his heels are 3 attractive young cheerleaders (yes they are in uniform). Just when it looks as if the guy was going to get away he stubbles and the lead girl grabs his shirt tail. This allows the other 2 to catch up where they start viciously punching and kicking this guy and kneeing him in the middle (maybe trying for the chestnuts). The girls are screaming at him at the top of their lungs. Above the screaming you hear him say in a pitiful voice, “But I wasn’t talking about you! Please stop!”. With that one of the girls picks up his binder and starts bashing him in the head with it. You look around and you are the sole witness. What would you do? Get in your car and go about your way? Go try to save this guy? Go get help to save him? Whip out your camera phone can load it to YouTube later when you get home?