I used to think that "Australian Rules Football" didn't actually have any rules.
Actually, I'm still not entirely sure on this one...
;)
A childhood belief about sport

others believed things like this
- I used to belive that the law was a number of rules on a notice board outside Buckingham Palace.— Nathan Vasey
- When I was little, I used to believe that football players really had shoulders that big.— Angie
- I used to believe that a football ref's flag was a banana peel.Anon
- When I was a kid, I used to think that the only way you could play football was if you had giant shoulders.— Sam
- I used to think that the Hunchback of Notre Dame was a football player.— Wendy
- I used to believe that a hat trick in football was achieved when a player scored a goal with their head!— Andy