In the United States, the National Football League, National Hockey League, and National Basketball Association represent the most well-known leagues for professional football, hockey, and basketball. However, lesser-known rival leagues can often pose significant antitrust challenges to established professional leagues. Let’s look at two of the most important cases that address rival-league antitrust challenges.

I. American Football League v. NFL

The NFL was created in 1920. From the 1920s...