Does your son have any siblings or is he a lone child?
If he has siblings, does he play fight with them all the time and do they get rough?
Quite often, children with siblings are just playing, but when they are playing with single children it often is misinterpreted as violent, rough, harsh, aggressive, because single children dont know how to deal with this kind of behaviour (unless they have a good group of friends.)
You need to have a meeting with the school anyway to establish why his behaviour is so different to that at home, or is it a case of you dont notice it at home (Im not getting at you but I know some parents dont notice that their kids can play very rough and get shocked when pulled up on it).
You need to understand what the problems are, what the triggers are, who the triggers are, and then have an agreed plan for school and home to deal with these issues.
If he is having to stay in, this wont help get rid of the aggression, tension so he needs to understand that he needs to behave in order to play outside.
It is better to try and resolve the problems before changing schools, especially if in general you are happy with the school. Some families end up moving their children from school to school and this does not help the child, so I would try and get to the bottom of it and sort out the problems now while he is still young enough to adapt.