Loads of athletes, including football players, are vegan. Jurell Casey, Arian Foster, Wesley Woodyard, Ricky Williams, a bunch of boxers and UFC fighters, Georges Laraque, Venus Williams and a whole bunch more. There's no reason that you can't build and maintain significant muscle mass on a vegan diet and there's a lot of evidence that suggests it has a bunch of additional benefits.
And there is also a large amount of data to counter some any claim that going vegan is anything remotely optimal for performance sports. It's not, and it's foolish to believe that just because any one particular athlete can do it, so can everyone else.
Far too many people want to go vegan after watching game-changers, and it's infuriating. Pushing aside the Director James Cameron's obvious conflict of interest when directing that film (a multi-million dollar investment is plant-based protein company), the science behind vegan diets being beneficial for performance, AND HEALTH, is incredibly flawed.
The bias is strong, and misleading.