
31. B.J. Penn
It’s never a good look when a champion leaves a fight promotion. That’s because they can’t claim to have the best athlete in the world anymore. However, the UFC found themselves in this situation with Penn after he defeated Matt Hughes. It was a major shock when he submitted the former champion. But an even bigger one when he signed with K-1 to kickbox in Japan.

Then the UFC immediately stripped him because they said that it was the same as vacating his title. Penn sued the promotion because he cited the Ali act. In the end, he fought several times in Japan before returning to the UFC. It was one of the most dramatic contract holdouts in MMA history. Penn’s legacy also impacted other fighters becuase it set a precedent for the UFC (via Sherdog).