pruni
HE WILL GROW OUT OF IT
honestly, I have seen kids go through this. Mine have, but esp dd (2).
A violent 4 yo does not = wife beater in 30 years. Honestly.
What is probably happening is that he wants to play a certain way with the other kids, or not at all, and they want something different, and somehow he lacks the skills to convey this. Or he is actually a bit shy.
So from what you have said here and in the past I'd guess its a combination of strong will (and this is a Good Thing) and not knowing how to articulate this. And also, being 4, not much caring about other kids he really barely knows, given that kids do usually take longer to get to know each other and trust each other.
ONE thing I would say is that some kids set each other off, and in this situation its probably best to avoid them if at all possible-he IS still learning social skills at this age.
My kids have a vile habit of fighting with the kids of the people I like best, and getting on with the kids with the absolute dullest mothers. I recently had to suffer a 3 hour discussion on the merits of b&q vs homebase, and I am trying not to hold it against ds.