The 1916 and 1943 Philadelphia Athletics
Connie Mack is easily one of the greatest managers in baseball history. The Hall of Fame skipper coached the Philadelphia Athletics to nine American League pennants and five World Series titles. Incredibly, his career in Philadelphia spanned 50 years from 1901 to 1950. Even more incredible, this gold-plated winner and baseball legend also holds the record for two of the longest losing streaks in the game's history.
In 1916, just two years after he took the Athletics to the World Series, Mack presided over one of the most dreadful end-of-season performances by any pro baseball club, before or since. The A's dropped 56 out of their last 60 games, including a 20-game losing streak [source: Gonzalez]. The final 1916 record was 36-117. It would signal the start of a seven-year slump in which the Athletics came in last in the American League every season.
While the rest of the country slogged through the Depression, Athletics fans had a lot to cheer for in 1929 and 1930, when Mack lead his Athletics to back-to-back World Series titles. But as Mack is famously quoted as saying, "You can't win them all." And from the mid-1930s through the mid-1940s, the A's lost many more than they won. In 1943, Mack matched his 1916 season with another 20-loss streak, ending the season at 49-105 [source: Baseball-Reference].