1986 World Series
Game 6 of the 1986 World series, Boston Redsox vs New York Mets. New York is batting in the bottom of the 10th inning. There are 2 outs and Boston is ahead. Then, 2 errors by Boston, including the famous "ball through the legs" by Boston's Bill Buckner, allow New York to come from behind and win the game.
And now, here's a re-enactement by a group of students in Kenya.