There's a ton of regional interest in niche sports, all of which have been mentioned here:
Southeast: College baseball, women's gymnastics
Midwest: Wrestling
Northeast: Lacrosse
West: Volleyball, water polo
What's the next BIG national sport? People keep trying to sell kids on computers playing eSports, but where's the audience? The younger generation wants to do stuff, not watch stuff.
I think lacrosse is making some inroads another places because it's an appealing avenue for wealthy families. They can create high barriers to entry and dominate the travel teams. I've heard of people in Toronto choosing it for being the best path to Ivy League admission.