Depends on what stakes you’re fighting for. If you’re fighting for status and don’t intend to kill each other doing things that can cause permanent injury like biting, eye gouging, etc. are socially unacceptable escalations of violence. The purpose of the fight is to establish your legitimacy and masculinity through an act of ritualized violence. It’s explicitly not supposed to result in permanent disability or death.

Same thing with fencing, where you’re not allowed to tank a hit so you can kick someone’s knee in to pieces then suplex them. That would be a socially unacceptable escalation of violence.

If you’re actually trying to kill someone then all bets are off, but in many contexts fights are about asserting dominance or proving yourself or waving your dick around, not killing your opponent.

Of course all those rules and norms go out the window pretty easily. As far as I know any social conception of a “clean” fight; fists only, no kicking, no blows below the belt, no headbutting, and you stop as soon as the other guy goes down, that just doesn’t exist anymore. If you throw a punch you should expect the other guy to shoot you. America is a savage and lawless place with little culture to speak of, and certainly no community or social organization left that can establish and enforce social norms of behavior.

Biting and scratching are likely seen as socially unacceptable because they leave jagged wounds that heal weird and are more likely to cause infection

If you’re fighting to not be killed then it’s fine but if you want to avoid being charged with something you probably shouldn’t stick your thumbs in someone’s orbits