S.T.
i gather that when he was younger you allowed this behavior?
i'm glad you're rethinking it!
first of all he must learn very firm boundaries around what he's allowed to do to other people. had that been my son he would have been summarily removed from the soccer field, no questions asked. can you imagine how the mom of the other kid felt at seeing her child menaced like that?
he does need to be allowed to express himself. fairness is an important thing for children to learn, so good for you for teaching your child about it. but the world has inherent imbalances and kids also have to learn to deal with this unshakeable fact with a degree of equanimity. they don't have to like it but they shouldn't come unglued over it.
start teaching him some coping techniques. let him express to you his anger and frustration over unfair events. reward him for both righting wrongs when he can do it calmly, and walking away when he can't.
and remove him inexorably from situations that he can't cope with.
khairete
S.