Pretty sure this happens all the time in boxing, martial arts, and even in other sports, seen firsthand in a local tournament how one team threw the whole game and their chance at lifting the trophy cause the match was apparently fixed and they are bound to get a pretty good sum of money guaranteed if they'd just throw the game and let the other team win, we found out it was fixed because there was the difference in skill and overall enthusiasm while playing just changed all of a sudden when they were steamrolling every other team in their bracket and the closest ones previously.
Is it illegal? You can say that, does it ruin the essence of the sport? Yes if you'd ask me. The main reason why we have these types of competitions in the first place is to cement who's the best and who's the strongest athlete or player, and having matchfixing scandals like these destroys the reputation of the sport and the league where it happened in general. But can we really stop it? Nope. It's a systematic flaw that would not be vanquished anytime soon cause people want money, people want certainty, and if that certainty can only be achieved through throwing matches or whatever, they'd be asking you for the pen and where to sign on it without a second thought.
Game fixing is still not totally eradicated in any sports up until now. So yeah, I believe, it is still happening but most of the time, people are just silent about it. Why? Because it is hard to prove if only few people know about it. How can you get evidence of the act? People will talk but it is all talk. This is why you will only hear murmurs but no tangible evidence can be presented.
But if you know the players or athletes involved and know how they perform inside the ring or arena, you will see if there is something wrong with the game. You can see that they are throwing the game. Just like one of the threads here before stating about a local basketball game. The audience clearly saw what was happening because they knew the players involved.