Don't assume a noisy few are the majority.

That guy is a peice of shit.

There's always some garbage in any community. It looks like, overall, people are alright. Most of Lemmy I've interacted with are great people, but there obviously are horrible people here too. There's no way to avoid it really. You can block/ban them, but they can always make new accounts somewhere.

100% agree.

I see two triggers that might have caused this either he was rejected like you said or he reached a boiling point from her provoking him.

Either way it doesn't excuse his behavior in any way. He attacked her. I hope he is arrested and prosecuted.

The guy is clearly a dangerous asshole with anger issues and his violent actions are completely reprehensible. He should be doing community service and taking therapy at a minimum, prison if she's seriously injured (she appears to have hit her head on that bench at the end there - scary shit).

Everything below with a pinch of salt since we lack a lot of context - we don't know what was said and what their relationship is (I'm not taking the social media post by the woman's alleged friend at face value for now).

The man is definitely the one who deserves most of the blame in this interaction, but the woman is not innocent and I'm confused with people in this thread seemingly implying that she is.
She initiated the physical confrontation and never seems to try to deescalate. She may be a badass, but she also has bad judgement. I don't want her to be still and demure, but I also don't want people to think it's a good idea to pick fights and prolong them.

She grabs his drink while he's trying to bring it to his mouth - this starts the physical altercation and could be interpreted as an act of aggression (realistically the guy just had his anger flare up and decided to splash it in her face - this is not self defense and I'm not defending it; but is it an escalation? Hardly, I think).
She then escalates by trying to slap him (inadvisable) and he pushes her back (this legitimately looks like self defense and is the only action in this entire incident that seems somewhat justifiable).
He kicks her after she falls down - escalation, malicious, indefensible.
As he appears to attempt to disengage (grabbing his stuff and turning to leave) she gets up, grabs an empty bottle and confronts him, holding it like a weapon. I doubt he was actually fearing for his safety but what was she thinking? Here it would have been quite useful to have audio for context. That said, she doesn't raise the bottle for an attack nor step closer to him, so he could still (and should have!) disengage from the encounter.
(One could argue she picked up the bottle to defend herself but I'm skeptical - why did she walk all the way over to him instead of waiting for him to leave, as he appears to be trying to do?)

Instead he goes ballistic and pushes her by the neck hard enough that she's thrown backwards to the ground, hitting her head on the way down. This is a major unnecessary and indefensible escalation of violence and should really make him liable in court. He could have killed her for Christ's sake!
Again, we don't know what was said but my guess is she said something that angered him which triggered him into pushing her - absolutely reprehensible on his part if this is the case.

Lessons for everyone:

• don't be a raging asshole
• don't push people in urban settings - it's much more dangerous than you think
• don't start fights with people, especially if there are no witnesses that could intervene when things get ugly
• if someone is trying to leave a fight, let them