1. World War I. Each team played 10 to 20 fewer games than originally scheduled, and the start of the 1919 season was also postponed.
2. Warren G. Harding's death. The MLB's entire schedule for the day after was postponed, as were all games scheduled for Aug. 10, the day of Harding's funeral.
3. World War II. Preparing for a season amid a war, the NFL shortened each team's 1943 schedule to 10 games.
4. D-Day. President Franklin Roosevelt asked MLB Commissioner Kennesaw Mountain Landis to keep baseball going to offer Americans a distraction during the war.
5. MLB strike of 1972. Baseball's first strike came in 1972, when players went on strike.
6. MLB strike of 1981. MLB players went on strike for the second time in 1981, this time over free agency.
7. NFL strike of 1982. The NFL Players Association went on strike three times prior to 1982, but that season would be the first time the NFL missed games over a labor dispute.
8. NFL strike of 1987. Though it was shorter than the strike five years earlier, the NFL's 1987 stoppage may have been more contentious.
9. NHL strike of 1992. The NHL's first labor-related work stoppage ended up postponing 30 games.
10. MLB strike of 1994 and 1995. The longest work stoppage in MLB history began in 1994.
11. NHL lockout of 1994-1995. The NHL played the 1993-1994 season without a collective bargaining agreement.
12. NBA lockout of 1998-1999. The first NBA lockout that resulted in cancelled games started in July 1998 and didn't end until January 1999 – spanning over 200 days.
13. Sept. 11 terrorist attacks. The terrorist attacks on Sept. 11, 2001, brought nearly everything in America to a halt, including sports.
14. NHL lockout of 2004-2005. The 2004-2005 NHL season was completely wiped out by an owners' lockout, as they wanted to institute a salary cap, which the players pushed back against.
15. NBA lockout of 2011. In their collective bargaining agreement that ended in 2011, NBA players received 57% of basketball-related income from the league.
16. NHL lockout of 2012-2013. Another labor dispute shortened the 2012-2013 NHL season from 82 games to just 48.
17. COVID-19 pandemic. It is too soon to know the extent to which the sports world will be affected by the coronavirus pandemic.