I'm not trying to define a minority sport, I'm making a strong case for Ireland's most successful sports achiever, Katie Taylor. Based on her accumulated Olympic, World, European and European Union titles (15 major titles in ten years) I think there is no competition for my nomination.
For the World Snooker Championship, just completed a small number of elite players out of 130-ish registered players participated in the final stages having won through preliminary matches.
Snooker is a minority sport defined perhaps by the number of elite players. On the other hand, based on the interest it generates it might be considered mainstream. Darts, croquet, badminton, squash, clay-pigeon shooting, fishing, rowing, cycling etc might be minority sports at a competitive level based on the number of elite competitors, but there is huge interest in them.
So what do you mean by minority sport?