Most tax cheating is from deliberate—actual or willful—under-reporting of income. This is called tax evasion—the most commonly charged tax crime. It appears that Diaz did worse than under-reporting. He didn't report at all.
"I just have to do the best with what I have," Diaz said following his UFC 158 loss to Georges St-Pierre. "You know what? I've never paid taxes in my life, no joke. And no one wants to hear that kind of talk and what's going on with me. I might as well just be a kid. I've had fight after fight after fight after fight, and you don't know what that does to somebody who didn't graduate high school. Take it into consideration for a second what three fights a year will do to you your whole life. And the only time you have some time off, it's not like it's a vacation – everybody's telling you you're this piece of s---, you're suspended, you ain't fighting this guy, you ain't fighting that guy, you have to come back and dance around a bunch of hard hitting people. It's a rough sport."
Diaz is close to 30 years old and he has competed in over two dozen cage fights. With over a decade in the sport, he has earned a nice chunk of change for fighting.
If he has truly never paid taxes in his life, that will surely result in jail time if he doesn't get the situation taken care of.
"What's sad is, he better go pay his taxes," UFC President Dana White said of Diaz following the UFC 158 bout against St-Pierre. "He came out publicly tonight and said he's never paid taxes in his life? Holy s---. That's sad. You wanna talk about sad? That's sad. Somebody better handle that with this check and make sure that kid doesn't end up with nothing. There's a guy who's Nate and Nick's lawyer and seems like a decent guy looking out for them. I'll probably give this guy a call and tell him, 'Nick said he's never paid taxes in his life, and you probably want to start working on that f---ing Sunday morning, not Monday morning.'"
Diaz didn't seem sure that he wanted to retire following a lopsided loss to St-Pierre, in the main event of UFC 158.
"I just feel like I fought everybody that I set out to fight," Diaz said. "Johny (Hendricks) here, he's a new guy. Jake (Ellenberger)'s been around for a little while. But I just feel like I've taken care of everything I wanted to do in the sport. This is hard stuff. I don't ever get any time off. I've only had a year off one time, and it was a stressful year. I was pretty bent out of shape that I didn't win that (Condit) fight. Nobody ever assured me, 'They're going to give you that (St-Pierre) fight.' I was just sitting around depressed the whole year off. I can sit here and make a million excuses about why I wasn't ready for the fight. But I want a rematch. I think I could beat you. I think I may be a better matchup for Anderson Silva, as well. But we'll see what happens. I didn't really have a good first round. I just think I could've been a little better prepared for this fight. I think next time, if I did get an extra shot, I think people would try to help me out a little bit."