a fan
A fan is someone who thinks they played every sport in high school, but they’re just a sad guy who watches the games from the side.
My neighbor is a fan of basketball. He says he played it in high school, but he’s just a guy who sits in the stands.
My dad is a fan of football. He thinks he was a star player, but he just watches it on TV.
My brother is a fan of soccer. He claims he was the best, but he can’t even kick a ball properly.