I agree with French, I would have talked to the kid after to see if he was alright and then probably his parents. If his parents have had previous problems with this dude then you could serve as a wittness for them to take further action if necessary.
I don't agree with people saying a "real man" this or that BS. 99% of people would have been stunned with shock before they could react in which the situation would probably be over and done with.
