Calvinball

And every time I would play serious tackle Nerf Calvinball out in the park somewhere, it played over and over in the back of my mind -- what would I do if I broke an arm?

1996 June 17, Wayne Lockwood, "Nobody without health insurance is a slacker or a loser", Knight-Ridder

At first my humans very much disliked it when I played croquet with them.... But eventually they decided to accept my participation, and renamed the game “Calvinball,” after the game of some comic book character

1998, Chris Glaser, Unleashed: The Wit and Wisdom of Calvin the Dog, Westminster John Knox Press, →ISBN, page 71

They are required to play the game of Nomic, in some form, or alternatively, the games Calvinball or Mao, which are basically the same.

2005, The Grate^([sic]) Book of Moo, Church of MOO, Lulu.com, →ISBN, page ccclvii

A more unusual sport is calvinball, which involves spontaneous rules that are never the same twice.

2006, Lee Mothes, The New Island Relocation Guide: How to Live on the Island of Possibility, →ISBN, page 50

Chick Lit, and pretty much all of publishing, plays a lot like Calvinball. There aren’t any rules.

2006, Cathy Yardley, Will Write for Shoes: How to Write a Chick Lit Novel, St. Martin's Press, →ISBN, page 148