The idea that an MMA champ would spontaneously call out another is ignorant. There are so many behind-the-scenes things that would have to be negotiated and agreed upon before a fight between, say, GSP and Silva would take place, and if one of them called out the other before knowing all of these, it would be really stupid of them. In fact, there would be 100s of people that would know about the "call out" a long time before it happened. Things that would have to be decided in advance of calling another champ out: 1) Date of the fight, weight, place 2) Share of PPV back end, other payments 3) Who walks out first 4) Contract restrictions pre-fight to ensure no injuries (common in all the contracts, but new stipulations would need to be added because a catch weight title fight would be such a massive event) 5) Pre-fight agreements on immediate rematches and other areas (i.e. pre-fight agreement on what happens if one fighter if there's a No Contest -- how would purse money be split, etc) There are other things that have to be agreed upon by both camps, the UFC, the network, sanctioning bodies and others long before one champ calls another out. With so many people involved, there would certainly be a lot of credible leaks, and the UFC would probably just have to announce it in advance -- you'd never get a "surprise" call out. Champs have been part of the fight game and know all the back office stuff very well, and they've been coached to never call another champ out (there's no problem calling out a contender in the same weight class) without going through the details with all the different parties. This may have happened in the past, but today MMA is too big a business for one champ to act spontaneously about something so important.