The Dodgeball Incident

The Dodgeball Incident was an event that happened to Edd was first referenced in the episode "Ed in a Halfshell" it is not seen in the series but according to Edd a stronger kid probably hurt Edd badly during a game of dodgeball and he has since feared going to gym class yet he surprisingly is seen in gym class in "Ed, Edd n Eddy's Hanky Panky Hullabaloo" and "Cool Hand Ed". It is probably the reason why Edd hates most sports.

Quotes
Eddy: [shows ball with bucktooth Edd drawing on it] "But's it's got your face on it, Double D." Edd: "Listen to me, Eddy!" [Eddy prepares to throw the ball] "Eddy?! It's gym class all over again!" [wails]
 * Edd: "Eddy, wait! I-I have a history with this game. I-what's that? Deep flashes, Eddy, like tentacles! Strangulating every rational nerve! Oh, I'm reliving it, Eddy!"