Green’s Dictionary of Slang

sluggers n.1

[slug v.2 (1); such whiskers were orig. a sign of a pugnacious fighter, stereotypically Irish]

(US) whiskers that extend from the ear to the chin, typically worn by a stage Irishman.

[US]F.P. Dunne Mr Dooley in Peace and War 211: He was [...] standin’ out on th’ steps in th’ cold, combin’ his whiskers – he wears a pair iv sluggers – with his fingers.
[US]Green & Laurie Show Biz from Vaude to Video 7: Irish characters wore ear-to-ear chin beards, called sluggers or gallaways.