Calvanball 

someone's stupid misspelling of Calvinball, an imaginary game from the Calvin and Hobbes comic strip

Calvanball was used in defining Jickball.

Calvanball by OutsideLookingIn July 17, 2010

Calvinball 

A game or activity where one player makes up the rules, can change the rules at any time, and doesn't have to tell you the rules (unless you break a rule, of course).

The Supreme Court Is Playing Constitutional Calvinball

Calvinball by JusticeCalvin June 29, 2022

Calvinball 

game in which there is only one rule, that being "you cannot repeat any action."

"Baseball is so organized. We should go play Calvinball!"
"Nothing is less organized than Calvinball."

Calvinball by Lionél Dripps April 15, 2004