The Parent Trap

My day off.
My Wonderful Wednesday Writing Day was interrupted by a phone call from the school to say that Eldest Son had punched a child in the face and thrown him to the ground and the child had hit his head rather hard.
I don't know how to handle shit like this, I really don't. My creative parenting juices so don't seem to flow that way.

I don't know what to think. Why the heck would he do that? There are a couple of thoughts going through my mind. He's almost 14, he's hormonal, he's a boy, he started boxing lessons last night... Now - it's the boxing lessons that stick out most in my mind at the moment.
Was he trying out some of the moves he's seen, imitating what he was doing with the boxing bag last night?
And for the record - the boxing lessons were supposed to be for fitness, not actually for boxing!
I don't know what to think right now. But I know this, if the school had phoned me to tell me that my child had been punched in the face and thrown to the ground, I would have been down to the school faster than a flash of lightening. In fact, I have had to deal with this kind of thing before, when Middle Child was being bullied by a rather big boy, who had a rather large mother, who actually chased my kids down the road (another story that was!) And when I felt that it was not being dealt with by the school, I went roaring down there like a smoky, diesel truck!

And now? Now it's my child doing what is totally unacceptable. Apparently he thumped this boy because he took his seat. Really? Is it possible that he can think that he can attack someone because of something like that? I can't think of a good enough reason to attack anyone, but for taking your seat?? Was he trying to show off, is there a history between him and this boy?
I have so many thoughts whirling around in my head. What is the best approach? Which are the right words? What kind of punishment? What do I do that will make the right impact?

What to do, what to do, what to do...?
Help me, somebody!!!!
I want my Mommeeeeeeeeeee.............!!!!