Okay. Thats so weird though. I have been around alot and I have spent alot of time with punks aswell. Obviously some of them had a pretty aggressive stance, while others where pretty pacifistic. But I havent met a single person that would punch a girl for no reason and then get slapped afterwards without even fighting back.
The only scenario that comes to my mind is, that he behaved like an asshole a while ago and punched a girl and some days or weeks later that dude in the white shirt gives him a visit for revenge and suddenly he got small balls. It still looks so weird.
But if that the case, both of them are utter shitholes. I give a small benefit to the guy in the shirt if the punk guy actually punched his GF for no reason, but you cant really judge without knowing the whole story.
Something similar happened to me actually.
I got in a verbal arguement with a girl and she made it physical. For pushing, then trying to slap/punch me. She wouldnt stop after I told her a few times to stay back, so I grabbed one of her arms and got behind her, holding her so she cant slap me (I didnt twist her arm or anything, I didnt inflict any pain or anything, I was just hold her arms tight to her body so she cant attack me.
I then told her again to stop attacking me and 10 seconds later I stepped back but at that time her boyfriend was already running towards me, wanting to fight me. Some of my friends and people I didnt know instantly stepped between us so he couldnt reach me and we fortunately managed to clear it up.
So yeah, it always needs the full context. If he punched the girl after she punched him for example, fuck that bitch, stop attacking people if you dont wanna get punched.