Through the 2008 season, the Tampa Bay Rays have the worst lifetime winning percentage of any MLB team with .417 (742-1037).
As of 2013, the baseball team with the worst winning percentage since 2000 is the Baltimore Orioles, with a 0.431 winning percentage.
Former NBA Vancouver Grizzlies. : From 1995 to 2001 these pathetic "athletes" compiled a record of 101 wins and a staggering 359 losses for a winning percentage of 21.9% : Case closed!
The New Zealand rugby team, the All Blacks, have an all-time 74.49% winning percentage.
Ron Guidry posted a .893 winning percentage which was the highest in baseball history by a 20 game winner.
1982-83 Philadelphia 76ers have the best winning percentage in NBA Playoffs history at .923 (12-1).