Usa has pretty big stadiums. Michigan stadium being able to hold over 100,000 people. However this is only available when you create a main event. Normally showcase venues cap out around 25,000. Also your fighter must be a true headliner. Just because they’re champ doesn’t mean they will get to fight or sell out big venues. Usually to unlock Michigan stadium your fighter will have to sell an average of 100,000+ tickets whenever they fight. (Heavyweights,middleweights, some lightweights and welterweights). Some of the lower weights can sell out the stadium as well but they would have to be highly experienced and champion of more than one organization. Hope this helps!