Boston Red Sox
The curse was said to have begun after the Red Sox sold Babe Ruth ("The Bambino") to the New York Yankees in 1919-1920. The Red Sox had been one of the most successful professional baseball franchises, winning the first World Series and winning 5 World Series titles but after the sale they failed to win the World Series for 86 years from 1918 to 2004, and the previously lacklustre Yankees became one of the most successful teams.