I don't think he "earned" it. I think he got a huge amount of money for having whatever brains he had left beaten out, for the entertainment of some crass people who find it entertaining... and all the money came from advertisers who paid to place their adverts in the vicinity so that all the crass people watching it could subliminally take in the "value" of the adverts. THAT is why he got money... because violence and beating someone draws a crowd. He didn't *actually* earn it.
As for whether or not he should or shouldn't give it to charity, I agree that he is under no moral obligation to do so whatsoever. HOWEVER, I do believe that by giving a large portion of his money to some worthy cause, such as a university researching cures for cancer, say, he will in fact contribute to humanity, and justify his existence, and earn a place in history.
As he stands, he is a worthless human being, of no more value than a hobo who stands on a street corner ranting in a drunken stupor; of entertainment value at best. Like hollywood actors, prostitutes, strippers, and anyone else who makes a living providing entertainment services, he does nothing for humanity apart from providing them with a few hours' respite from the awful mundanity of their own hamster-treadmill existence. He is panem et circenses. He distracts humanity from achieving anything more than funding the capitalist machine, from questioning their government, and from improving their own lives. At best he, like any sportsman, is a clown, at worst a parasite who takes money from the unwashed masses watching him assault someone else.
Whilst I can appreciate that it took years of practice and discipline to achieve such great skill in being able to assault someone, I do not see that assaulting someone is anything to admire. At most we can admire his persistence in his desire to assault someone.
Before you respond with criticism, or "ass", or similar responses, please be prepared to answer every one of my points above, and next time you feel like posting memes about consumer culture, waste of natural resources, or conspiracy theories about the government, remember, you're part of the problem, if you think watching sports and encouraging people to compete in sports is OK.