Rules cannot be used twice (except for the rule that rules cannot be used twice), and any plays made in one game may not be made again in any future games. The game may involve wickets, mallets, volleyballs, and additional sports-related equipment.
There is only one permanent rule in Calvinball: players cannot play it the same way twice. For example, in one game of Calvinball, the goal was to capture the opponent's flag, whereas in a different game of Calvinball, the goal was to score points by hitting badminton shuttlecocks against trees using a croquet mallet.
Calvin created the game when he first became tired of organized sports. Although the first depicted game of Calvinball followed Calvin's failure to join the baseball team , the game appears in such a complete form there that it is likely that Calvin and Hobbes had been playing the game for a long time beforehand.
The only hint at the true creation of the game comes from the last Calvinball strip, in which a game of football quickly changes into a game of Calvinball. Calvin remarks, "Sooner or later, all our games turn into Calvinball," suggesting that a similar scenario led directly to the creation of the sport.
Although all games of Calvinball are different (as players can make up rules as they go), many of them seem to involve a volleyball (the "Calvinball"), masks, and pickets with numbers printed on them.
Key features of various games have included (in approximate order of appearance):
- Wickets (referred to as "time-fracture wickets" in one strip)
- Soccer balls
- Small signs with numbers
- The "Opposite Pole" (when a player touches it, everything becomes the opposite; a player must declare when he or she touches it, but because it is the "opposite" pole, the player declares touching it by not declaring it)
- The "Very Sorry Song" (see below)
- The "No Song" zone (a player doesn't have to sing the "Very Sorry Song" if he or she is in the "No Song" zone)
- The "Bonus Box"
- Croquet mallets
- Badminton shuttlecocks
- The "Invisible Sector" (this sector cannot be seen, and whoever wanders into it must cover their eyes; the only way out is to be bonked by the Calvinball)
- "Vortex spots" (if a player steps in a vortex spot, they have to spin around until they fall down)
- The "Boomerang Zone" (if a player incurs a penalty while in the boomerang zone, the penalty is instead suffered by the player who called them on it)
- A volleyball (the "Calvinball")
- Trees (as goalposts)
- Non-numerical scoring values (such as "oogy," "boogy" and "Q")
- The Calvinball theme song (see below)
- Water balloons
- Hobby horse
- The "Pernicious Poem Place" (a player caught in this area must recite a poem and incur a penalty relating to the poem-ice cold water)
- The Bag Flag Zone
- The Secret Base
- Being forced to move and speak in slow motion
- The Perimeter of Wisdom
- The Corollary Zone
- The Baby Sitter Flag (any player touched by the Baby Sitter Flag must obey the baby sitter)
The Calvinball theme song made its only appearance in the penultimate Calvinball storyline. Calvin sings the lead while Hobbes sings backup with "Rumma-Tum-Tums."
- "Other kids' games are all such a bore!
- They've gotta have rules and they gotta keep score!
- Calvinball is better by far!
- It's never the same! It's always bizarre!
- You don't need a team or a referee!
- You know that it's great, 'cause it's named after me!"
No sport is less organized than Calvinball.
Sooner or later, all our games turn into Calvinball.
The only permanent rule in Calvinball is that you can never play it the same way twice!
The score is oogy to boogy!
The score is still Q to 12!
In one strip, Calvin landed on the Pernicious Poem Place and was forced to recite the following poem to Susie:
"This is a poem! Please do what you're told! And here is a bucket of water, ice-cold! Please take this water, and dump it on me! Don't hesitate, do it A.S.A.P.!
In one Calvinball strip, Calvin stole Hobbes' flag, and Hobbes hit him with the Calvinball. As a result, Calvin was required to put the flag back and sing the "Very Sorry Song."
The "Very Sorry Song" has two parts, one sung by the one who did the action (the "offender"), and one sung by the person whom the action was done to (the "victim").
Offender Victim "Here's the 'Very Sorry Songg.' Won't you help and sing alongg?" "Bum bum bum" "I blew it!" "He's sorry!" "I knew it!" "So sorry!" "I'm very very sorry that I took your precious flaaggg!" "Just don't do it any more, you scurvy scalawaaggg!"
The scoring system in Calvinball is never made clear, and it's unlikely that it has a consistent scoring system across games. The only detail that is known is that scores can have non-numeric values. In one game, the score was Q to 12 and in another, the score was oogy to boogy.
- Bill Watterson once said, "People have asked how to play Calvinball. It's pretty simple: you make up the rules as you go."
- In one strip, Calvin and Hobbes are seen playing an obscure combination of croquet, cricket, and baseball. It is unknown whether or not this is a variation of Calvinball, a predecessor to Calvinball, or simply another obscure game.