Did they deserve it?
The middle class yuppies in their 4x4 had it coming. It wasn't their beach, it was the kids', and the kids had every right to be pi**ed-off with the invaders who thought they could just turn up and demand they turn their music down.
It was the yuppie bloke that started all the trouble by confronting them, when all the kids had done was turn up at their favourite place with their bikes and dogs to hang out.
The kids were the locals, the yuppies were the invaders. The escalation was entirely the result of the yuppie trying to show off to his girlfriend by being macho. The moment he touched the volume control was the moment he declared war - which is always a bad idea if you're a) on someone else's territory and b) outnumbered.