The Tournament that Nobody Remembers is the name given to the Quidditch World Cup of 1877.
While the evidence is that something, possibly the tournament, took place, no one has any memory of playing any matches or even of being there at all. Worrying incidents such as team members showing up in another country entirely or with body parts missing, enmeshed the wizarding world in conjecture and conspiracy theories that continue to this day. The tournament was therefore “re-staged” the following year (QWC).
From the Web
WizardingWorld.com (Pottermore) features:
Writing by J K Rowling on Imgur (Daily Prophet coverage of the 2014 Quidditch World Cup, originally from Pottermore):
Harry Potter Wiki: Quidditch World Cup