Dude didn't even let his wife call the cops, that would've been the least he could've done. Also, if he started getting pounded on, surely his wife would've reacted and contacted the police or security, right? He still would've been right simply because they hurt his little boy. No policeman can condemn you for punching a man who hurt your kid...right? Personally, I even wonder myself if the guy's friends would've reacted at all if they saw their friend getting a well deserved punch.
I most certainly would not protect my friend for pushing a child to the ground, heck I'd roughen him up instead, as would you all I expect. I'm just saying that if there's a time for a man to be violent, that was it.
I respect a man for not fighting back in front of his child if HE was the one who got hit. Not if his kid was the one who suffered the blow, whatever happened to protecting your loved ones.