Deliberate mistake: In the basketball scene against Camp Mowhawk, the Mowhawk players' shorts have been pulled down a little, making it easier for the Camp Northstar players to pull them down all the way.
Meatballs (1979)
1 deliberate mistake - chronological order
Continuity mistake: When Bill Murray is running from the basketball game to get on the bus he's wearing a sport jacket - a second later when he gets on the bus he's wearing just a T-shirt.
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Suggested correction: The jacket is right next to Bill on his left side.
The Stomach: What? No mustard?
Trivia: The original title for Meatballs was "Summer Camp." No one seems to remember the reason for the title change.