When to fight and When to walk away?

Today my son gets home from school and says there was a huge fight at school between the Mexican gang kids (who don't even go to their school) and the Tongan kids, apparently from what I gathered the Tongan kids walked out of school when school was done and some other kids told them that those kids are asking about them, they (the visitors) walked up to the kid standing near my son and asked who he was they exchanged names one kid tried to hit the other kid and missed and the my sons friend pretty much did the rest, David grabbed his friend and tried to hold him back but things escalated past that and a big brawl pretty much happened, my son David kept grabbing his friend and saying "C'mon we don't need this use your head, walk away" But one thing led to another and police were called and everyone was called to come back to the school to give statements.. While I was in the V Principal office she thanked David for using his head and staying calm during the fight. She asked David what happened and David told what he had saw which matched the statement he had given. I asked her what the other statements had said she informed me pretty much the same as what David had said. She told me that both sides agreed that David did not fight and was trying to stop it on both sides. I asked her what are our boys suppose to do when someone from a different school comes and tries to hit them first. She answers they are suppose to walk away and get help... This answer has me confused.. Will the person they are fighting let them walk away? Or will he attack them from the back? She told me that the opponents in the fight were much smaller then my son and his friends, which led me to the question Who's fault is that they came to my sons school looking for a fight? Every question I asked her she answered with "I have to just go back to the size of the opponents"... What kind of answer is that, the OTHER kids as she called them came to THEIR school looking for them and wanting to fight them they came with friends they threw the first punch and because they GOT beat up the Poly kids in the fight are all in trouble.. Walk away? When, How? How can one walk away when someone is punching you, or how will you know they WILL let you walk away? I really think the POLY kids in this case got the CRAP end of the deal because of their size... I don't think fighting solves anything, but I believe sometimes and with some situations you can get really hurt if you don't fight back...
I've told my son he did the right thing he pushed his little brother back into the school for safety, and he helped his friend.. I've been told by the school cop it probably would of been worse had David not grabbed everyone and got them out of the fight situation.. I'm thankful the Lord kept my son and his friends safe... Do I think there should be a punishment YES, do I think that the punishment given to the boys fits the crime... NO....