The word backyard itself is used as an adjunctive noun (not an adjective) when paired with another noun, e.g. backyard barbecue, backyard mechanic. The word backyard is not an attribute in either case.
Depends what backyard.
in your backyard
My backyard My backyard
No, backyard isn't an adverb. It is a noun, and may be an adjunct in terms like backyard barbecue.
backyard fish culture
it depends in what type of backyard you have.
Our Backyard was created in 1984.
a barbecue that goes in your backyard
No, it is a noun. But it can be used as a noun adjunct with nouns as in "backyard barbecue" and "backyard mechanic."
in his backyard he built a small garden
backyard monsters hacked