Due to a misunderstanding, a game was played in Huddersfield last weekend between Rugby League team Huddersfield Thickos and Rugby Union side Leeds Numbnuts.
The cause of the gaffe has been traced back to a clerical error where the Thickos were accidentally placed into the Rugby Union league in 1963, where they have been playing ever since.
Thickos fan Geoff Munt said, "For my whole life the Thickos have been living a lie, playing Rugby League in a Rugby Union league. I can't believe that nobody noticed."
It isn't the first time that such a thing has happened. Last year's Rugby League World Cup was won by Australia's Aussie Rules rugby side, and the Six Nations was won by an Irish Gaelic football team.
"There's so many similar sports," said BCC sports commentator Geoff Whistle. "It's not surprising the organisers make the occasional balls-up. In a way, it's part of what makes sport so interesting."
Whistle is hosting next week's British Formula 1 race at Aintree.