Denver
Denver is a city that can consistently and enthusiastically support three professional sports teams. Unfortunately, it has more than that—the Colorado Rockies, Colorado Avalanche, Denver Broncos, Denver Nuggets, and Colorado Rapids (soccer). Until recently, the Nuggets and Rapids had been the odd teams out, as the Rockies, Avalanche, and Broncos have all reached or won championships in their respective sports. But here and there the Nuggets have come close to catching up, and fans patiently await their year.
What's great about Denverites is that most aren't just spectators. After a game, they go out and do stuff—hiking, bicycling, kayaking, and, yes, playing team sports themselves. The city and its proximity to outdoor pursuits encourage a fit lifestyle.