What was Grusha's career-ending accident/injury?

It's mentioned in SV and the website that Grusha used to be a top snowboarder until he ended up in a accident that injured him so bad that he had to retire, but I don't see what that injury may have been. He walks fine and can battle well enough to be one of the highest-leveled Gym Leaders in Paldea (and considering how intense Pokémon battles allegedly are, that's a great feat), and there really doesn't seem to be any sign of physical damage or crippling injury on him. I get that in real life there's invisible injuries, chronic pain and other such disabilities, but this is a fictional world with loud and expressive designs that communicate a lot of each character's traits, so it's weird not to show it on Grusha and get us some clearly disabled rep in Pokémon as a bonus. He never even mentions this injury in-dialogue afaik, and things like still being called ″the Sub-zero Shredder″ makes it seem like this is just some translation shenanigans, but maybe I'm just missing something. Does anyone know if the game ever clues in on what happened to Grusha?