We know that athletics is corrupt from top to bottom and large scale drug-taking has been covered up. We know that drug-taking in cycling was endemic and was covered up. We know that football in even places like Italy is totally corrupt. There's evidence that football in Spain is corrupt, with decisions being given in favour of Real Madrid & Barcelona. There has been proven match-fixing involving referees in Germany, although not in the top division.
In Eastern Europe, Africa and Asia, corruption is endemic, involving bookies, referees, players and other officials. Apparently even our 3-2 win in Munich a few seasons ago was investigated by Interpol on suspicion of match-fixing, which put Pellegrini's assertion that he didn't realise we'd win the group if we scored another goal into an entirely different light. Referees have been quietly moved out out the front-line in the PL a couple of times. We told Riley that Mason would not be acceptable to referee our games in the first PL winning season and Riley stood him down. Why would he do that unless we had good reason to insist?
There's so much money involved both in terms of broadcast revenues and gambling that it's incredibly naive to declare there is no corruption. There is but people would prefer not to see it.