C19: origin obscure; originally applied to ruffians in New York who attempted to exert political pressure
Word Origin and History for plug-ugly
n.
"ruffian," 1856, originally in Baltimore, Maryland, from plug (n.), American English slang name for the stovepipe hats then popular among young men, + ugly.
[origin unknown; perhaps fr rowdy fire companies in Baltimore, hence fr fireplug; perhaps fr New York toughs of the 1830s who wore top hats over their ears as helmets; perhaps related to plug-muss, ''a fight,'' found by the early 1950s]