Well definitely not his red hair I have a red hair boy who would not hurt a fly, for some reason his red hair seems to make him a target at play centres for other bullies

Some kids just have trouble expressing how they are feeling and they act out.
Some kids are over stimulated. It could be anything like diet related or playing video games not age appropriate.

It's really hard from afar to know what is going on, I have a GF with a little boy who was rough. She is gentle, he has an older sister who is calm and gentle, it's just who he is. He has heaps of energy.
It could be a rush of hormones for some boys, I think it's at around the age of 5 or 6 they get a big injection of male hormones.

Steve Bippuph was a big help for us when it came to boys, he explained a a true life story of a young boy who was misbehaving, his Dad was a truckie and not home alot. The Dad changed jobs and was home alot more and the boys behaviour changed dramatically in the right direction.

It's one of those things, until you walk a mile in someones elses shoes, you just never know.

I don't mean to direct my comments at boys, it can be either.