From the formation of baseball's National Association in 1871, more than 2,950 teams in over 200 leagues have competed in various professional sports. Some, such as the National and American leagues in baseball and the National Basketball Association, have prospered for decades. Others, including the roller hockey (a.k.a. roller polo) New England Polo League (1883-1884) and the National Bowling League (1961-1962), have long since been forgotten by...