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. Masks must be worn at all times in Calvinball; these are not allowed to be questioned.
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 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, (you make up the rules as you 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" (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
- "Vortex spots" (the player who steps in one has to spin around until they're dizzy)
- The "Boomerang Zone" (A decree is returned to the player who called it and they must do what the decree says instead)
- The "Invisible Sector" (This sector cannot be seen and whoever wanders into it must close their eyes; the only way out is to get bonked by the Calvinball)
- A volleyball (the "Calvinball")
- Trees (as goalposts)
- Odd Scoring (Oogy to Boogy, Q to 12, etc.)
- The Calvinball theme song (see below)
- Water balloons
- Hobby horse
- The "Pernicious Poem Place" (The player caught in this area will be forced to recite a poem followed by a penalty relating to it)
- The Bag Flag Zone
- The Secret Base
- Slow Motion
- The Perimeter of Wisdom
- The Corollary Zone
- The Baby Sitter Flag (The babysitter calls the game to an end and puts the other players to bed)
Calvinball theme song
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!"
After that, Calvin tells Rosalyn to "feel free to harmonize with Hobbes on the 'rumma-tum-tums'".
The "Pernicious Poem"
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.!
The Very Sorry Song
In one strip, Calvin and Hobbes are playing Calvinball, and Calvin "[steals]" Hobbes' flag, and Hobbes hits him with the Calvinball. As a result, Calvin is 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!"
Obscure Point System
Nobody knows how to score in Calvinball. The only known point values are Q and 12 in one game between Calvin and Hobbes and oogy and boogy in another.
- 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.