My brother and I and our GF's were walking downtown Portland (Oregon) ran into a situation like this but it was a younger kid that the 5 other teenagers were beating up. My bro's GF had pepper foam spray so we ran over sprayed the whole group and started beating the shit out of them..it was hilarious.
These "tough guys" started crying and screaming like the little bitches they are..it was basically different variations of - "dude wtf, wtf dude we didn't do shit to you....aaaaaaaawww my eyes fucking burn..I can't see!!!! (cough cough) my eyes... gawd dammit, get off me"..
Transit police showed up and arrested all of them since my girl got the whole thing (them beating the kid, not us beating them) on her iPhone. BTW, if you are beating someones face into the concrete train platform and miss, the pepper spray foam that was coating your fist from their face, will burn like hell when you scratch up your knuckles from the occasional missed throw.
What concerns me more about these video's is that no one even tries to step in. Punks.