For every multi-billion-dollar league that has succeeded, that are 10 professional sports leagues that failed. History is littered with attempts to start a new pro sports league to rival the NBA, NFL, NHL or MLB. Whether because of timing, money or talent, the failed pro leagues listed here just couldn't stick around.
To keep this manageable and to discuss only leagues that people might remember, we're looking only at the American professional sports leagues that started and ended in the 21st century. There was a time in 2001 when the XFL was supposed to be the next big thing. And at one time, all these failed leagues thought they would be, too.
Vote for the biggest failures, and feel free to add any defunct professional sports leagues not listed here.
The XFL was a professional American football league that played its only season in 2001. The XFL was operated as a joint venture between the World Wrestling Federation (now the WWE) and NBC.
Ended: Ceased operations midseason in 2019
The Alliance of American Football (AAF) is a professional American football league, founded by Charlie Ebersol and Bill Polian.
The United Football League (UFL) was a professional American football league based in the United States that began play in October 2009 and played four seasons, the most recent being cut short in October 2012.
The Championship Gaming Series was an international esports league based in the United States, with teams from several other countries.
Pro Cricket was a professional cricket league in the United States. It was operated by American Pro Cricket LLC (APC), a private company independent of the ICC and the USACA.
The Professional Rugby Organization, known as PRO Rugby, was an American professional rugby union competition. PRO began play in April 2016 with five teams and ceased operations by January 2017.
The Fall Experimental Football League (FXFL) was a professional football minor league that played two seasons in 2014 and 2015.
Major League Ultimate (MLU) was previously one of two semi-professional Ultimate leagues in North America, the other being the American Ultimate Disc League.
The Xtreme Soccer League (XSL) was an indoor soccer league that began play in December 2008. The XSL folded in July 2009. Although the league officially called it a one-year hiatus, it never resumed play.