The Colorado Avalanche, as all NHL players do, must wear suits to games. This includes onto the plane as they travel for road games. (My understanding is that many of them change into sweat suits once they’re on the plane itself.)
Now, before I got into Colorado’s sartorial success, I’d like to address this custom of wearing suits. I don’t believe it’s in their contracts. I don’t think they could be fined or benched for not wearing a suit. If one of the veterans wanted to go all Dustin Byfugilen and throw the unsuitable clothing into the showers, that would be up to him.