(unofficially via http://www.bartel.org/calvinball/ and http://calvinandhobbes.wikia.com/wiki/Calvinball)

Permanent Rule: You may not play the Calvinball the same way twice.

Primary Rule: The following rules are subject to be changed, amended, or deleted by any player(s) involved. These rules are not required, nor necessary to play Calvinball.

1.0. The following words in these rules are mostly freely interchangeable, the Primary Rule applies:

• Can
• May
• Must
• Shall
• Should
• Will
• Would

1.1. All players must wear a Calvinball mask (See Calvinball Equipment - 2.1). No one may question the masks.

1.2 Any player may declare a new rule at any point in the game. The player may do this audibly or silently depending on what zone (Refer to Rule 1.5) the player is in.

1.3. A player may use the Calvinball (See Calvinball Equipment - 2.2) in any way the player see fits, whether it be to incur injury upon other players or to gain benefits for himself.

1.4. Any penalty legislation may be in the form of pain, embarassment, or any degradation the rulee wishes to execute upon the other player.

1.5 The Calvinball Field (See Calvinball Equipment - 2.3) should consist of areas, or zones, which are governed by a set of rules declared by players. Zones may be appear and disappear as often and wherever the player decides. For example, a corollary zone would enable a player to make a corollary (sub-rule) to any rule already made. Or a pernicious poem place would require the intruder to do what the name implies. Or an opposite zone would enable a player to declare reverse playibility on the others. (Remember, the player would declare this zone oppositely by not declaring it.)

1.6 Flags (Calvinball Equipment 2.3) shall be named by players whom shall also assign the power and rules which shall govern that flag.

1.7 Songs are an integral part of Calvinball and verses must be sung spontaneously through the game when randomly assigned events occur.

1.8 Score may be kept or disregarded. In the event that score is kept, it shall have no bearing on the game nor shall it have any logical consistency to it. (Legal scores include 'Q to 12', 'BW-109 to YU-34, and 'Nosebleed to Pelvic Fracture'.)

2.1. Mask - All participants are required to wear a mask

2.2. Calvinball - A Calvinball may be a soccerball, volleyball, or any other reasonable ball. Bowling balls are accepted.

2.3 Calvinball Field - The Calvinball Field should be any well-sized field, preferably with trees, rocks, grass, creeks, and other natural obstacles.

2.4 Miscellaneous - Other optional equipment include flags, wickets (especially of the time-fracture variety), and anything else the players wish to include.

3.1 Before, During or After the Game the Calvinball Song can/may/must/can't/may not/mustn't be sung:

“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!”

(Backup-Singing “Rumma Tum Tums”)

3.2 Calvinball quotes include but are not limited to

“feel free to harmonize with Hobbes on the Rumma-tum-tums” (Calvin to Rosalyn)

“No sport is less organized then Calvinball” (Hobbes)

“Sooner or later, all our games turn into Calvinball.” (Calvin)

“The score is still Q to 12!” (Calvin)

Although all games of Calvinball are different, 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, Soccer balls, Flags, Masks, Small signs with numbers, Songs, Zones/Sectors, The “Opposite Pole”, The no song zone, The very sorry song (see below), The “Bonus Box”, Croquet mallets, Badminton shuttlecocks, “Vortex spots”, The “Boomerang Zone”, A volleyball (the “Calvinball”), Trees (as goalposts), Buckets, Poems, Sacks, The Calvinball theme song (see below), Decrees, Water balloons, Hobby horse, The “Pernicious Poem Place”, The Bag Flag Zone, The Secret Base

Special Thanks to the Calvinball Founders Bill Watterson (who is also owner of the Calvin & Hobbes Trademark), Calvin, and Hobbes.