Playing in Someone Else's Sandbox
|See also:||Transformative Work, authorial intent, shared universe|
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Playing in Someone Else's Sandbox (or in "someone else's backyard") is sharing others’ creativity/intellectual property via the creation of fanworks: fanfic, cosplay, vidding, scantalation, RPGs, fanart, fan films, and much more.
"Garden," "Backyard," "Playground," "Universe" are variations fans themselves employ. Another variation is "playing with someone else's toys." The addition of the word "play" and "toys" perhaps suggest that fandom and fanworks are fun by definition. "Play" may also suggest childish, or at the very least, something not as serious as "work."
This "sandbox" may be a professionally-created canon universe, one owned by TPTB. It may be a universe or characters created by another fan.
This sharing may be an involuntary collaboration, a recognized collaboration, and it may be a completely invited one.
Those involved in this participatory and transformative culture understand that someone else has created the text/world, and that they are but that the creator no longer has the final say over their creation.
Examples of Use
Mercedes Lackey: Having established that I am a Good Guy for letting you play in my sandbox, following in the footsteps of my mentor Marion Zimmer Bradley, let me continue. Some folks have been horribly incensed because I asked, politely, that you not post Valdemar fanfic over in Prodigy, because that service lists itself as a PUBLISHING SERVICE and not an information service, and it is a FOR PROFIT entity. This was to protect YOU." (December 1992) 
Lucas knows we're playing in his sandbox — he once even had a panel set up to read the zines to ensure that nothing he considered unfavorable got through... 
I think plagarism in fanfic matters, definitely. It's not a monetary issue, because almost everything is being borrowed... I think of it as misbehaving in the sandbox, so to speak. We're all here to play, and even if it "doesn't really matter" in the long run, it makes things less fun, it makes people angry, and it makes the author feel hurt. 
We're all playing in the same sandbox and I'm happy to share my sand. Would love to see what you do with it! 
Fandom is a big happy sandbox and I am totally willing to share my toys! ^_^"
"Garden," "Backyard," "Playground," "Universe"
One variation is Marion Zimmer Bradley's 1980 statement:
I regard myself not as the “inventor” of Darkover, but its discoverer. I others wish to play in my fantasy world, who am I to slam its gates and in churlish voice demand that they build their own? If they are capable of it, they will do someday. Meanwhile, if they wish to write of Darkover, they will....Or, look at it this way. When I was a little kid, I was a great lover of ‘pretend’ games, but after I was nine or ten, I could never get anyone to play them with me. And now I have a lot of fans, and friends, who will come into my magic garden and play the old ‘pretend games’ with me. 
Another is the fan quoted by Lucasfilm in one of 1981's Open Letters to Star Wars Zine Publishers by Maureen Garrett:
I suppose I have a rather simplistic view of the subject. If George Lucas and his friends come to my house and went out to play in my backyard, I'd expect them to abide by my rules that you don't stamp on the fuchsias, play basketball in the vegetable garden or tear fronds off my eight foot tall Tasmanian tree fern.
It's a big sandbox that we're playing in; if you don't want to share your toys at least don't pick on the other kids. 
The sheer anger when people realize, "She's playing in our playground, using the very same toys that we use, BUT SHE'S NOT ONE OF US," is astounding. 
Fandomination.net was founded based on a set principle of ethics. This affects to a degree the material that we allow. It is our belief that if a professional author objects to people playing in their universe and playing with their characters that we, as fan fiction writers, should respect those wishes. 
Sailor Moon fan Moon Momma/The Housekeeper also references a garden in her 2001 essay about why fanfiction should adhere to canon as strictly as possible:
Yes, fanfiction is about exploring the possibilities. Within reason. We fanfiction authors are not creating our own characters and our own worlds; we are using characters and stories and ideas that were created by someone else. We owe the original creators the courtesy of treating their creations with care and respect; it's their garden we're playing in, as uninvited but tolerated guests.
People who would say that these are the real characters are pulling up carrots from the Sailor Moon garden and trying to convince the reader that they're eggplants.
When we're playing in someone else's garden, it isn't nice to uproot the plants. Instead, we should treat them carefully while admiring their beauty. And hope to heck we don't get sued for being there.
- Queen's Own, Mercedes Lackey newsletter, December 1992, Archived version
- from Southern Enclave #38 (Winter 1994)
- from Does plagiarism matter in fanfiction?
- jelazakazone, AO3 Profile.
- JumpingJackFlash, AO3 Profile, posted March 4, 2013.
- Bradley, "The Keeper's Price 7" New York, DAW books, 1980, page 14
- from Queen's Own (Mercedes Lackey newsletter)
- from Untitled post on Cousin Jean's proposal: "She's taking advantage of fandom's communal history of caring, and I think that's abusive"
- from the FanDomination.Net's Terms of Service
- Orthodoxy vs. Exploration