Sleephead - you made three mistakes!
1 You confronted the little sh... er darling. You should NOT have done so!
2 You hit him first. You should not have done so!
3 You did it in front of witnesses. You should not have done so!
If I may suggest, if you need to confront the attacker, make sure he's alone! After all, he's a coward, mummy has to help him! And if you do hit him, hoof him in the taters first!
Not that I wish to encourage any untoward behaviour of course!
I hope you get this sorted out, and the bully gets what he so richly deserves!