Bowling, and the differences in bowling balls are far more dramatic than the mostly-marketing-hype differences in golf balls.
Although of course there are plenty of sports where players can use their own apparatus… tennis rackets, racing bicycles, racehorses, just to name a few.
Golf balls definitely are more tightly regulated. In neither one does an opponent have to do anything with that ball, it’s not that much different than the variation in golf clubs and baseball bats.
And of course football makes a federal case out of imagined differences in the inflation pressure of footballs.
There’s not much to compare it to, but boxing has the odd rule of the Standing 8 Count. A referee can decide a boxer who is sufficiently hurt should be treated as if he was knocked down even though the next punch might actually knock him down, and counteracts the very rule that says if a boxer is unable to continue he should get a Technical Knock Out. It really makes no sense and there are no sensible guidelines for it’s use.
As I already pointed out, boxing is rare in allowing the rules of the sport to be negotiated by the participants. The size of the ring, weight limits, size and type of gloves, facial hair, judges and referees, and even the number of rounds can all be contracted. World title fights have standardized the number of rounds at 12, but that only happened about 20 years ago, before that both 12 and 15 round title fights were held, and going back more years there was no standard, and before that fights had no limit to the number of rounds, resulting in draws when enough people got bored after the 50th round of inaction.
This is a place where viewpoints get challenged, and for me this has always been a double-edged sword. I hate me-too bleat-along message boards; I want healthy discussion and a variety of perspectives. On the other hand, I often find that my original intentions get…skewed a bit.
Anyway…
TriPolar - I have never, ever, in my life seen a boxer (at any level) get so much as a dirty look for clinching. Not breaking promptly when ordered, hitting out of the clinch, the occasional ear bite, yeah, absolutely, but never the grab itself. Heck, I’ve never seen a video game where clinching was illegal, and we HATE that crap. Could you post a link of some kind? I’m actually kinda morbidly curious now.
Robot Arm - Athletics definitely comes the closest, but it’s not quite on the same level as swimming. What Owens and Lewis did were landmark achievements from the legends of the sport. (Same for that female track star who got 3 golds and 2 bronzes; don’t remember anything else about her, sorry.) Swimming regularly produces multiple medal winners simply because there are so many to go around.
I should also add that swimmers don’t have to worry about running into their opponents and are less prone to injury, lessening the chance that a favorite will get knocked out by some terrible fluke. I’ve seen that more than a few times on the track.
Ulf - Thanks for your elaborations. Honestly, I had no idea exactly how many events there where (I only knew that there were a LOT); I wasn’t implying that each stroke had all the same distances. But the fact remains that every permutation that exists is a medal event.
Oh, and I wasn’t complaining. There are some who have, but I don’t feel like digging them up right now.
I can’t name a case right off hand, but I’ve seen fighters warned for holding, and had points taken away for excessive holding. Granted, it doesn’t happen often, it’s usually ignored because it doesn’t really help a fighter win. Keep in mind that boxers are expected to work their way out of simple clinches. If they don’t or one fighter is clearly just holding, then the referee is supposed to tell them to break. If they don’t do that the referee will attempt to physically separate them. The problem is that a clinch has both fighters holding and there’s no point in giving out equal penalties to both of them. Simply being in contact with each other doesn’t make a clinch or a hold, there has to be an attempt to keep the other fighter from punching.
ETA: The first fight described on this page had a point taken away from Mark Johnson for holding, affecting the outcome of the fight.
Maybe already mentioned, but there are only a few sports where a low score is the goal such as in golf. Low times are the norm for races, but lowest score is limited to a few sports.
Is darts the only sport where you start with a score and count down?
Golf and cross-country were mentioned upthread. Got others?
Darts was just mentioned. I don’t know of any others.
Do runners even really try other events or do they really concentrate on just one? While there are a lot of people who get two medals in swimming, it’s rare that people get more then one. Most people concentrate on one stroke and distance.
Is golf the only sport where people can lose after they win? There’s the well known case that Craig Stadler got penalized for a rule violation after the round was over.
Runners try a lot of events, I assume you mean do they try non-running events? I don’t think many people start out attempting to be a decathlete, some of them must be runners who were willing to try other events. If you mean non-track and field events, I suppose not too often.
At the world class level, runners stick to a narrow range. 100/200 guys will not be running the 800.
100/200 guys won’t have the aerobic capacity to run the 400 though you do see the 200/400 double(Michael Johnson, for one).
The big divide is 400 t0 800. Alberto Juantorena(Cuba) was the last male 400/800 double at the Olympics.
Other typical track doubles are 800/1500 & 5,000/10,000. Often the 5/10 guys run the marathon though only Emil Zatopek ever won the marathon and a track race. He actually is the only 5/10/marathon winner in Oly history. And he did that in one Olympics.
Decathletes usually find they’re mediocre at a lot of events. 
They tend to be sprinters/power athletes with a bit of endurance. The 1500 is usually their weakest event.
There’s an absolute classic Olympic Story from 1900. In the Teams Cross Country event, the British were pretty sure they would beat the French (the only 2 teams who entered), but they only had 4 runners - and a team had to have 5. So they needed someone who would just turn up, run, and finish last - his 10 points and the (much lower) scores of his teammates would still be lower than the French team total.
Anyway, the British Team approached the Australian Stan Rowley (yes, Australians considered themselves British back then - Sons of Empire, etc). Rowley was no mug - he won bronze in the 60m, 100m and 200m. But it’s fair to say, cross-country running wasn’t really his thing.
The race was 10 laps of a 500-metre course. After 1 lap, Rowley was leading. After 2 laps, Rowley was walking. After 3 laps, Rowley was lapped.
Some time passed…
The spectators knew full well what was going on, and cheered Rowley in his endeavours. There are rumours of champagne and cigars being consumed mid-race. Eventually, the officials decided they wanted to get home that evening, and so stopped Rowley after 7 laps and awarded him 10th place. Stan Rowley - Olympic Gold Medallist.
So there you go - there really was a Gold medal that your Grandma could have won.