Through the 2008 season, the Tampa Bay Rays have the worst lifetime winning percentage of any MLB team with .417 (742-1037).
In 1979, the worst Super Bowl team was the Los Angeles Rams. They went in to the playoffs with a winning percentage of 9 to 7.
In 1912 when the team was called the Highlanders, the team record was 50 - 102. for a .329 winning percentage. Since the team was named the Yankees in 1913 the worst season was 1913 with a record of 57 - 94 for a .377 winning percentage.
Through the 2007 season, the team with the worst winning percentage on MNF is the Cardinals with a record of 5-12-1 for a winning percentage of .277. The Falcons are second worst at 9-21 for a winning percentage of .300. The Bears are third worst at 16-34 for a winning percentage of .320. The Bears 34 losses is the most of any team on MNF.
As far as winning percentage goes, the Bulldogs went 1-5 in 1904 and 1905 for a winning percentage of .167. Since they have been playing a regular season of 10 or more games, it is a .273 winning percentage (3-8) in 1953.
The Vikings worst winning percentage for a season came in 1962 when their record was 2-11-1 for a winning percentage of .179. The most losses in a season was 13 in 1984 when they went 3-13 for a winning percentage of .188.
Since the AFL-NFL merger, the worst division winning record was 7-9 by the 2010 Seattle Seahawks.
Seattle Seahawks .500
The NBA team that has the worst winning percentage right now is the Sacramento Kings. There winning percentage is .217 and there record is 15-54. They are currently 26 and 1/2 games back from making the playoffs in the Western Conference, and 39 1/2 games back of the first place Los Angele Lakers.