Professional women's volleyball
Ultimately, when given the choice between going to watch male and female athletes, people tend to prefer watching men, with the notable exceptions of tennis, Olympic gymnastics, and Ronda Rousey. It'd be great to have a professional women's sport league that isn't treated like the little sibling of an existing league.
People love going to watch high school women's volleyball. So, why isn't there a professional women's league that pays? The prize money for the USA Premier Volleyball League seem like peanuts when compared to other sports.
There should be another attempt to start a professional women's volleyball league, potentially using NBA stadiums during the off-season. Volleyball is a fun, dynamic, team sport that's ripe for replays on Sports Center and exhilarating live. Previous attempts must have suffered from execution problems because there's nothing inherently limiting about the sport itself.