Calvinball is a game loved and played by millions. Well, actually by two fictitious cartoon characters, Calvin and Hobbes created by Bill Watterson. But it's still a game, regardless.

Calvinball can be described as a combination of hockey, football, American football, baseball, golf, badminton, and tennis and the rules to Calvinball are as follows:

• Anything you make up goes
• You can never play the same way twice

You can imagine how much freedom this gives you in playing the game and may also go some way to explaining why no one has ever played Calvinball with Calvin and Hobbes.