TL;DR: Basically, what is a clear and concise way of knowing when to let a girl go, and when to defend your ground against another man trying to get in on the action?

Body:

When do you ward off another man trying to get in on your action? It seems like TRP pretty much says that it is never worth getting into a physical altercation with another man over a woman. The mantra of "she's not yours, it's just your turn," is repeated and it almost seems like the view is that if a guy steals away a girl, then the girl let herself be stolen away. But what if the guy totally chumps/AMOGs you in front of a girl, and then she leaves you for him (or just leaves you in general)? It's not like a woman's love for a man is unconditional, and letting another man do that to you in front of a girl shows major lack of balls, and the ability to protect a woman if shit went down. Why shouldn't she leave you if you allow this to happen?

Scenario:

I am a 7 and she is a HB 9 (this is all hypothetical), she is a plate who has shown that she might be LTR worthy. Y'all take a trip to the beach. You go out to shred on some waves, and your girl stays to tan on her towel. You comeback into shore, and there is a guy hitting on her. Typically, he saw you guys come together and wondered "why is that chick with that nerd." Your plate listens to the guy, likes the validation, but tells him she has a boyfriend who is out killing it on waves at the moment. She says "thanks, but no thanks." The guy doesn't let up because he is determined and doesn't know if she is just shit testing him or not. I come back in from the shreddy, and make it known that I am in fact her boyfriend, and signal for him to leave. He still doesn't leave and proceeds to try and chump/AMOG me in front of the girl. I tell him "you need to walk away," and he holds his ground.

Question: Is it then OK to fuck this guy up, should I wait until he lays a finger on me or the girl, or is this still not grounds for fighting over a girl in the eyes of TRP?