This is a hard question to answer. You might say "Water Polo" or something obscure, but as soon as you could name an obscure sport someone else could invent a new one that would be completely unknown. "Least popular professional sport" might be something easier to qualify.
tennis or golf
none of the sports are least popular.
The least popular sport is volleyball i checked 100 sites no lie x
The least popular Olympic sport is football.
marbles, which is actually a sport
The most popular sport in America is Football.
i think the least popular sport is bowing or golf they both are BBBBBBBBOOOOOOORRRRINNNNG BUT ggggggrrrreeat for family game nite
The most popular sport in the US is football. Both NFL and College Football.