Green’s Dictionary of Slang

n.g. n.

[abbr. no good]

(US) a person or thing that is bad or inferior.

Tribe of Tammany 5: He [...] became a brawler and an N.G. [HDAS].
[US]C.L. Cullen Taking Chances 53: This nag [...] was sold as an N.G. last year.