Snooker and golf have traditions of self policing don't they? As does ultimate but then I understand that college ultimate in the us has referees.
There may be "arbitrators" during matches at the national tournament, but otherwise US college ultimate relies on the same self-enforcing "spirit of the game" concept.
In North American professional and most levels of junior ice hockey (not college or high school), fighting is, strictly speaking, against the rules insofar as it carries a five-minute penalty, but it's regarded part of the game and everyone knows it (we could to a massive thread just on that. In fact, I think we have). Even in college hockey where fighting carries a game misconduct and possible suspension with it, it happens. Some guys decide it's worth it for the psychological impact or their frustration just boils over.
Indeed, a players' penalty minutes are often regarded as a positive statistic. That's counterintuitive because, during the game, it's never really advantageous to take a penalty and go on the penalty kill. Exactly how much of a disadvantage that is will depend on the quality of the teams' respective special teams' unit.
A team that is on the penalty kill a lot is either playing dumb or, as often happens in college hockey, is taking a lot of interference and hooking penalties because they don't match up with the size and speed of the opposition. Same in lacrosse.
I suppose that since fights are usually offsetting penalties, a lot of PIM usually is the mark of a good enforcer/role-player/goon/team-guy. And, all things considered, a team that is never penalized at all is probably not playing physical enough. It's one of those things where if you don't occasionally go too far, you're probably not going far enough.
In basketball, even outside of the last five minutes where the trailing team deliberately fouls (that should be banned, I think), there are so-called "smart fouls." I recall an interview with Michael Jordan where he praised Larry Bird with being very good at choosing when to commit a smart hard foul. I think it's a bit like handball in this respect, although in basketball, players can foul out.
In baseball, there are rules that are routinely flaunted by tradition. The base coaches don't always stand in that box they're supposed to stand in. A batter can erase the back line of the batters box. The umpire has a lot of discretion on how much lip he'll take from a player or a manager (or the fans).
On a play at second or third, the defensive player can just swipe the dirt between the bag and the sliding runner without actually tagging the runner. This is an old convention. The alternative is the guy getting his hand spiked.