Intervention in a fight?

My son and I were at a strip mall buying some car parts on a Friday night. 4 skater teens started to mouth of an elder custodian emptying garbage can. Apparently the old man told these kids not to skate in this area because there were alot of women with strollers. The verbal became pushing and grabbing at the oldman's broom. After about 5 minutes my son just had it and he challenged the 4 teens. Then to my surprise within seconds he was all over them and there were some broken noses involve....My son took some beating as well. By the way, my son is 17 and has a black belt in Shotokan. The whole incident lasted about 5 minutes and mall security was there immediately to stopped the fight...Then the sherriff was involved...It was a mess.... I want to reprimand my son for being a hot head but in the meantime he stood up for the weaker. To be honest at that point, I can't help but to delay my invlovement, I wanted to see if he can really take down 4 aillents. Hard choice.