Google stuff like 'FBI Point Shaving' for an example of past and present cases.
Anyone who thinks a multi-billion dollar industry that is wagering goes without occasional black hat influence is naive as a small child.
Individual sports are MUCH easier to influence since you only have to get to one guy. Boxing was notorious for it.
Lets put it this way.
You're a middle card fighter, you make 16K to show, 16K to win, maybe you get a fight bonus or two a year.
You get three fights, you win two and lets say you bag a bonus. That's 100K+. Minus training expenses, trainer/management cuts, you might drop below $100K, but its a heckuva living for a guy who would otherwise be roofing.
Now, say your next fight, coming off a loss, is against a ream bum. Some promotional newcomer who never panned out, 0-2 thusfar, you're a -450 favorite. You can buy him for +375.
You can buy him by submission for +1100.
You can buy him in the 3rd round for +1600.
Suddenly, you have the potential to notch a half million (or more) payday on this one fight by pulling guard in the 3rd and 'accidentally' giving up your back, tapping, oops, got caught. Will get 'em the next time.
Meanwhile, cousins, brothers and wives are cashing out stubs in LV, collecting booked action from the locals, for a shitton...;
Middle card fighter 'retires' from the right game at 32-35 with a paid off house, maybe a coiuple cars and a hundred grand in the bank if he plays it smart.
He retires a millionaire if he plays it smart and dirty.
Now with judging, that's a different kettle of fish. That is probably something mobb'ish, since that would require a fairly creepy degree of influence to get to three people, simultaneously, like that, unless they've been in the bag all along. I know how it works. I've seen The Departed.