Calvin and Hobbes was nothing without Calvin’s endless imagination, which brought to life his toy tiger Hobbes, as well as their ongoing series of make-believe adventures. One other product of his imagination was a game called Calvinball, which is literally a game like no other. In Calvinball, players are allowed to make up completely different rules as they go along, and the only true restriction is that no rule change announced by a player can have been used in previous games.
Understandably, Calvinball might be difficult, at first, to turn into a real sport. Sports fans would never know what to expect from game to game, and referees would have to be intimately familiar with every single other Calvinball game that’s ever been played. However, this is the real secret to the potential success of Calvinball: players would be testing their minds via imagination even as they tested their bodies via a variety of different physical skills. There would be no room for anyone to ever get bored of the sport, because it would change and evolve from game to game. Besides, Calvinball has, over the years, featured pretty much every sports ball and bit of sports paraphernalia you can imagine, so Calvinball is a game that fans of any sport can fall in love with.