Green’s Dictionary of Slang

(US) a southern mountain farmer, a hillbilly.

1918		H. Simon ‘Prison Dict.’ in AS VIII:3 (1933) 31/1: RIDGE RUNNER. Originally an Arkansas, rather than a Kentucky, hill billy. Any uncouth stupid fellow.
1931		K.C. Times 10 Sept. [heading] Just Ridge Runners [DA].
1943		National Geographic Mag. May 596/1: They want to stalk us ‘ridge runners’ to see us scald a hog, or weave a rag carpet, or get baptized [DA].
1948		‘Army Speech’ in AS XXIII:1 Apr. 77/1: Hillbilly recruits were called ridgerunners.
1965		A. Green in Journal of Amer. Folklore 🌐 My personal vocabulary of such catch-names was enriched [...] to include ridge-runner, appleknocker, cherrypicker, and turdkicker.
1975		J. Carr Bad (1995) 163: One of these ridge-runners is gonna say something to me and I’m gonna knock the top of his head off.