The Curse of the Bambino was a famous baseball superstition that claimed the Boston Red Sox were cursed after they sold star player Babe Ruth — nicknamed “The Bambino” — to the New York Yankees in 1919.

After the trade, the Red Sox went 86 years without winning a World Series, despite several heartbreaking losses, while the Yankees became one of the most successful teams in sports history. Fans and media blamed the long championship drought on the “curse.”

The curse was considered broken in 2004, when the Red Sox won the World Series after dramatically defeating the Yankees in the American League Championship Series.

Wikipedia, The Atlantic, YouTube "The Baseball Explainer"