DS1 is Yr 7, so only been at the school a few weeks.
He's been going by bus with a yr9 boy (BoyA) who lives nearby. Boy A is a bit different, one of those children who's easy to wind up IYSWIM, he's told DS1 he has an illness that makes it difficult for him to ignore things (Aspergers?)
Events,as DS1 tells it, without any input from anyone else are:
They were on the bus home yesterday and Boy B (also yr9) asked Boy A if he wanted a fight. A did his best to ignore, but it continued with the addition of some swearing. DS1 wasn't near them on the bus, so doesn't know what was said/done to ellicit the "you wanna fight?"
All three of them got off the bus. DS1 and A crossed the road, as they need to to get home, B also crossed the road (which he doesn't need to) following them and continuing with the taunting and swearing. B has put his hand on A's shoulder and swung him round and which point A has had enough and punched B. There was just that one punch and they all went their separate ways.
B's parents have complained to the school and A has been excluded for 2 days. There has been no punishment for B.
DS1 is livid, as he feels it wasn't B's fault, he was defending himself and B started it etc. He wants to march into the head's office and tell him what happened.
What, if anything, should DS1 (or I) do?