Green’s Dictionary of Slang

backyard adj.

(orig. Aus.) small, trivial, insignificant, esp. of business conducted from one’s own home.

[Aus]Bulletin (Sydney) 1 Sept. 11/3: Of course, the habit of being found dead is a thing to be discouraged [...] but if anyone decides that it is really necessary to be found dead, then it is just as well to do it amid a set of curious circumstances as to do it in a sordid, ordinary backyard manner.
[Aus]Bulletin (Sydney) 1 July 22/2: What sort of backyard bushman is this ‘Harrison O.,’ who snorts with derision [...] at the Rev. Spurr’s story about an Australian girl running a dingo down on horseback?
[UK]C. Stead Cotters’ England (1980) 157: It’s all private self-indulgence, back-yard calumny.