Describe the methods that established professional sports leagues have used to thwart the success of new rival leagues in their sport. Provide evidence to support your response by referring to at least one the following cases: North American Soccer League

Describe the methods that established professional sports leagues have used to thwart the success of new rival leagues in their sport. Provide evidence to support your response by referring to at least one the following cases: North American Soccer League v. National Football League; Philadelphia World Hockey Club, Inc. v. Philadelphia Hockey Club, Inc.; United States Football League v. National Football League; American Football League v. National Football League; Hecht v. Pro Football.