And criminal prosecution.
Which reinforces my point, that as pointed out to the OP - you cannot contract away the right of the state to prosecute whatever it chooses to, and the risk they will succeed in their prosecution. the only guidelines are what is deemed normal (or in legal terms, “reasonable”), so therefore what the courts are likely to convict on. Many lawyers’ country club memberships have been paid for by arguing what “reasonably” reasonably means.
For example, the sort of fight that might be tolerated in a professional or university league between peers may become criminal if say, it was a neighbourhood pickup game where a 20-year-old beats the living daylights out of a 13-year-old. Like everything else in life, context is everything. OTOH, the same level of fighting in a professional baseball game would likely result very quickly in ejection and possibly assault charges. It rarely happens in football because of the greater opportunity for “accidental” corrective action to be applied during a future play.
You are factually incorrect that simple touching is not battery in some states, for example the state of Florida all that is required for misdemeanor battery is intentional touching, against the will of the person being touched. The state just has to prove that it was intentional, and that it was unwanted. Section 2 of the statute is an “OR” not an and - no harm of any kind is required
http://www.leg.state.fl.us/statutes/index.cfm?App_mode=Display_Statute&Search_String=&URL=0700-0799/0784/Sections/0784.03.html
What happens at fairs or concerts and such where people are bumping into each other all the time?
People jostling basically standing in place, or pushed by others would generally fail the “intentional” portion. Though say for example, pushing forward intentionally to reach the stage would be a chargeable battery in florida, if the victim and the state wanted to pursue it.
However, relevant to the OP, if in Florida you intentionally caused bodily harm, it doesn’t matter whether the victim gave their consent.
~Max
They do, but it can still be illegal.
Plenty of teenage girls and boys have pierced their own ears. A couple of girls talked some guy into doing it when I was in high school. They just did it out in the smoking area (yes kids, we got to smoke cigarettes in high school). You need a needle and thread, a potato (or some other backing when you poke the ear), and optionally an ice cube to numb the area and stop bleeding. You can leave in the thread to keep the hole open or just stick an earring in the hole.
I doubt such a thing has ever been prosecuted, as long as nothing goes wrong. I suppose if it resulted in some serious infection or transmission of disease it might get some notice.
Here’s a strange story that relates to the OP - a suicidal teen was charged with inciting his own murder.
The boy who incited his own murder | Crime + Investigation UK
Perhaps I’m just “an outside observer” 
but I myself have a hard time distinguishing between these two scenarios. ISTM you’re just phrasing the exact same thing two different ways.
If a guy’s only motivation to fight someone is that his culture “demands” it, that means he wouldn’t do it absent that cultural demand. And the force of the cultural demand is that if he violates it, he will pay a social price for doing so. So the first scenario boils down to the same thing as the second, but you left implicit some parts that you spelled out in the second.
Unless when you wrote “my culture demands” you really meant “there’s a cultural norm that I accept and share”. That’s something else. In that case, it’s not the force of the cultural demand making him fight the guy right now; he himself wants to fight the guy, and the culture is just what shaped his values to produce that desire.
Florida may say something different, but the general rule AFAIK (IANAL) is that the touching has to be both unwanted and threatening - that is, the victim has to feel that the action is intimidating or threatens violence. So someone tapping you while getting your attention to say hello would normally not be intimidating, but in the wrong setting -startled or on a dark and stormy night, for example - could be taken as such. Someone who jostles past you in a crowded venue, depending on how much effort they put into avoiding contact, may or may not. The guy who barges his way through knocking people over would likely be guilty. A person yelling at you and poking your shoulder is obviously threatening, particularly if physically stronger-looking or seeming unhinged.
This goes back to what I said earlier - there is no magic word or action that produces a bright line - your actions and how they are interpreted by the authorities are all that matter, and the same action may or may not be charged or prosecuted, depending on the mood of the enforcers, the whim of the judge, whether the prosecutor thinks the case is winnable or if the authorities have it in for you or your class of person, whether the victim wants to press charges, etc. Consent may go a ways to moving that line, but it does not erase it.
This is more or less what I meant. Some people internalize the mores of an honor culture. Some people do not, but rationally determine that going along with it is better than the punishment they will receive as a defector. The former group are consenting to fight, the latter group are not (legally).
Back in the Jurassic Era when I was in college, I took a single law class, which covered contract law. The attorney teaching the course said that courts generally don’t like to second guess contracts, but will void them if they find the terms to be unconscionable, which the attorney defined at the time to be “a punch in the gut.”
I presumed at the time that he was talking metaphorically, but in case he wasn’t, you may have your answer.