With the way the UFC pay’s their fighters, it is each athletes responsibility to pay their own taxes. The UFC isn’t taking out withholding’s for these guys like a salaried employee, which is why it’s important to pay what you owe come tax time.
The recently retired Chris Leben has apparently never done this, as told by Dana White:
“Chris Leben had some minor tax issues, which he is getting cleared up – minor in that he never paid his taxes. He’s getting that cleared up. [He owes a ]Couple bucks. Imagine never paying taxes and making a lot of money, how much that would be. That much.”
(quote via mmajunkie.com)