Hailey, It doesn't seem to be an idiom that anyone here recognizes. It's a mystery. Where did you come across this phrase? As a sentence fragment "Leave the horse alone" could have several possible literal meanings: It might mean that when the person responsible for the horse went away, the animal was abandoned. It had to survive on its own. Maybe it is a command not to bother the horse, to leave the horse in peace. or "Horse" is a slang word for "heroin". Maybe it is an warning to keep away from heroin. "Crazy Horse" is a brand of very strong malt liquor sold in the U.S. Maybe it is advice to stay away from that brand, which usually comes in a large 40 oz. bottle.

I say it's related to the idiom "to horse around," meaning: "To play around roughly with someone or something." As in: "Stop horsing around with your little brother." -> Leave him alone. So, when someone says, "Leave the horse alone," I guess he's just using the above idiom on a funny manner. We'd have to know to exact context, though, to be certain. "Leave the horse alone" is not an official idiom, at least. Since context is everything (especially for non-standard idioms), that phrase could also simply mean: "Don't touch the subject." As in: "Next meeting we should talk about getting a raise." "If I were you, I'd leave that horse alone for now."

The exact meaning would depend on the context: - If the horse is well-behaved, the person being spoken to might be molesting or bothering the horse. - If the horse is wild or bad-tempered, it could be a warning not to try and pet or feed the horse.

"Leave the horse alone", it is neither the English idom nor slang. It is a title of a modern literature written by Mahmoud Darwish, and it is translated by Jeffrey Sacks. ISBN 0-9763950-1-0 In this book's title is the one that six-year-old Mahmoud Darwish asked his father when he and his family were fleeing their village in Galilee to take refuge in Lebanon across the border, as the Jewish forces were advancing on Arab lands in Palestine... The meaning of "Leave the horse alone" is refering to the title of the book in English version.

Hmm, the 'heroin' link is an interesting one. I'm gonna up-vote you one, as I have a good feeling about it. :)