I second that.sjabbie wrote: And I really do think that every sports anime should have a category of it's own.
But AFAIK, for each of them there's only one anime made.
If you don't want categories with only one anime, maybe you could do it like this:
My point of view is that the main topic of any anime should always be categorized, even if it's the only one with that category. fe. Hikaru no Go definitely should be categorized with Genre::Action::Sports::Go. After all, it's what that anime is about; seems kinda silly to not to categorize it...
If that isn't acceptable, however, then at least do create that Genre::Action::Sports::Other as a catchall for all those less common sports...