Professional sports teams are athletic organizations comprising talented, expert players hired by club owners whose revenues originally derived from admission fees charged to spectators seeing games in enclosed ballparks or indoor arenas. Teams are usually members of a league that schedules a championship season, although independent teams also can arrange their own contests. The first professional baseball teams emerged in the east and Midwest in 1860s, most notably the all-salaried undefeated Cincinnati Red Stockings of 1869. The first league was the haphazardly organized National Association of Professional Base Ball Players (1871), supplanted five years later by the more profit-oriented National League (NL) that set up strict rules for franchise locations, financing, and management–employee relations (including a reserve clause in 1879, which bound players to their original employer), and barred African Americans after 1884. Once the NL prospered, rival major leagues also sprang up, notably the American Association in 1882 and the American League in 1901. Major League Baseball (MLB) became a model for the professionalization of football, basketball, and hockey, which all had short-lived professional leagues around the turn of the century. The National Football League and the National Hockey League of the 1920s were underfinanced regional operations, and their teams often went out of business, while the National Basketball Association was not even organized until 1949. Professional team sports gained considerable popularity after World War II. The leagues dealt with such problems as franchise relocations and nationwide expansion, conflicts with interlopers, limiting player salaries, and racial integration. The NFL became the most successful operation by securing rich national television contracts, supplanting baseball as the national pastime in the 1970s. All these leagues became lucrative investments. With the rise of “free agency,” professional team athletes became extremely well paid, currently averaging more than $2 million a year.