U.F.C. organization used their contract privileges to stop Nick Diaz from competing in the Worlds 2011. Nick is in negotiations to fight against Georges Saint Pierre and the organization blocked Nick from competing. His brother Nate however is competing in the brown belt division according to his coach and top competitor Caio Terra.
It is highly understandable for UFC to protect their interests and at the same time super commendable for the Diaz brothers to want to compete in their sport's biggest event. Big ups to all!