I was bullied for two years at a school in Liverpool. I simply thought that this tough guy was too much to handle. But he picked on me once too often when I'd suffered a very close bereavement over the previous weekend. I totally lost it with him and punched him really hard in the face a few times, then getting him into a headlock and on the ground. His tormentors that were egging him on tried to encourage him to fight on and one or two were slyly kicking me in the head. After I let him go, they persuaded him to have another go at me and although I'd calmed down when he punched me in the face all my anger rose up again and I did it to him a second time.
I'm not saying all this to sound macho. Personally, I can't abide fighting. I never could. But who knows what that lad might have had to endure in his personal life, aside from the lad who was bullying him? It was likely sheer frustration. He could easily have done the other boy serious harm, but I wouldn't be surprised if it's a one-off. I think we're all capable of doing serious harm when we're up against it.
I hope the injured lad is all right. I hope he has learned a valuable lesson too. Bullying is not nice.