In spite of the many promises made by Hollywood movies, fistfights are almost never balletic exercises in controlled violence after which the winner walks away and looks like a bad guy. They're usually terrifying, random encounters in which untrained, generally drunk people flail around until their friends pull them apart and the bouncer kicks them to the curb
Do fistfights have rules? There should be rules for fist fights. Is there an agreed upon set of standards for how much violence is appropriate?
There is a rule of fist fighting: Do not fight in a fistfight. Both your mom and your martial artist agree on this. There is a chance that there will be violence. Back down if you find yourself in a situation like that. Don't run. You should tell a monitor. It's stupid to go to jail, get injured, or even die over a spilled drink, so do whatever you can to get out of it.
Let's talk about what the rules and expectations are if you fight. The laws that apply to fighting in the streets are the closest we have to a set of rules.
Some people think that once hands are thrown, civility is gone, and you should go for crotch shots, chokes, and concealed weapons. Krav Maga emphasizes finishing a fight as quickly and efficiently as possible by targeting the most vulnerable part of your opponent's body. Even if they can't fully train their techniques in a full-contact sense, they can still learn them and use them to their advantage.
One of the problems with no- rules fighting is how to respond. He was training for life-or-death hand-to-hand combat because he was training for protecting Jews from Nazi militias. Do you really want to hurt or kill someone who takes a cheap shot at you at a bar?
Most fistfights involve a couple of drunk dudes puffed out their chests until someone takes a swing. The bouncer broke it up and threw everyone out. This is not the kind of situation where someone should be using potentially deadly force.
Since most fights are casual and no one wants anyone to die, are there rules? It might be possible. Like any group, people who fight all the time can develop a set of rules over time. Some tactics in a fight are not to be used by people who are honorable. This could be escalating by using a weapon, or involving other people to help, or it could be a more serious type of attack. These moves are not allowed in a mixed martial arts match.
There are a lot of precedents when it comes to following a set of rules in a fight. Duels to settle personal disputes have been going on since medieval Europe. They were only practiced among the wealthy and rarely fought to the death. The duelists were trying to find a solution to the conflict. Efforts were made, but sometimes this didn't work and people died.
Even without explicit guidelines, mutually beneficial combat rules can be created organically. A code called "live and let live" was developed by soldiers in World War I. If left to their own devices, soldiers often developed rules of equal reciprocity for attacks, signals for cease-fires, and even displays of military prowess, so that no actual attack was needed. The Germans reportedly fired until they cut a hole in the wall.
If you know the culture of the person you are fighting, then you might be able to get away with it. Most of us don't have a set of guidelines for how to conduct a fight in America.
We are left with an lassie-faire, anything goes situation in which it doesn't matter what, since we can't challenge people to duels with pistols or swords anymore. If you are going to keep to the Queensbury rules, your opponent can either pull out a knife or have his friends jump in if he starts losing.
If you want to win or lower your chance of serious injury, an "anything goes" style is the best option. The law may not see it that way.
If nothing gets broken, the peace isn't disturbed, and the fight is overseen by a police officer, mutual combat is not against the law. Cops won't intervene unless one party says they no longer want to fight or be injured. Unless it is a licensed fight like a boxing or wrestling match, mutual combat is not allowed in Oregon.
It's a mixed bag in the rest of the US. It is legal in most places to hold boxing matches or wrestling matches, but a fistfight is not. If you land a punch, you could be charged with assault, and you could also be charged with vandalising a window or murdering someone.
You are allowed to use force to defend yourself. Physical force can be used if you feel threatened. The force you use to defend yourself has to be justified. If someone slaps you at a bar and you stab him in the heart, it will be hard to prove it was self-defense.
If you follow fighting rules and testify that you stopped kicking him when he was unconscious, the judge will likely sympathize with you. I wouldn't believe it. Why didn't you show restraint before throwing a punch?
There are no rules in a fight against a stranger because you can only do what you want. If you engage in a fight, you could be injured or killed, and you could be arrested and imprisoned. It's not likely to be worth it if you choose to engage in a fist fight. Unless you hang around with immature 12 year olds, no one is going to be impressed.