Green’s Dictionary of Slang

half-ass v.

[half-assed adv. (1)]

(US) to hold back, to doing things by halves.

[US]A. Steinberg Running the Books 32: I’m not saying the community of my youth is loud and pushy. Only that they’re in earnest. They don’t half-ass things.
[US]C. Eble UNC-CH Campus Sl. Spring 2016 5: HALF-ASS — do with minimal or substandard effort.