8. Francis Ngannou
Ngannou is one of the most ferocious fighters on the planet. The giant Cameroonian possesses frightening knockout power. This helped him win the UFC heavyweight championship. He should be a promoter’s dream but that’s not how it turned out. The UFC refused to match his financial demands and one of the most bitter contract holdouts ever emerged.

They made him an offer and told him that if he didn’t like it, he could walk. Ngannou and his representative shrugged before nodding their assent. This left the UFC in an embarrassing situation because he flirted with boxing. He made the promotion appear to be cheap because they wouldn’t pay their star. Ngannou may be the winner at the end of all this (via Give Me Sport).