Having played Sunday League, amateur football at all age groups in my life, I really am not surprised that something like has happened, which says it all really and it's very sad.
You can sense violence close to erupting pretty much every week, whether it be aimed at officials or the opposition. Obviously 99.9999999% of the time nothing like this happens, but I've seen it so many times where one wrong decision, one bad tackle, one word said out of turn and all hell can break loose and there is no protection or security.
Some horrible people can play football at this level and there is no way to stop it happening. I know a few people who have been banned from playing for a certain amount of time, but they just continue to do so because the referee won't know, the venue won't know and the opposition won't know. If anything happens, give a fake name.