The Plug Uglies were an American Nativist criminal street gang, sometimes referred to loosely as a political club, that operated in the west side of Baltimore, Maryland, from 1854 to 1865. The term plug ugly was used to identify an extremely tough ferocious fighter who could give a sound beating to an opponent, with the Plug Uglies' name additionally stemming from their practice of stuffing oversized plug hats with wool and leather, pulling them down over their ears for head protection as primitive helmets during the numerous street battles they participated in. The name Plug Uglies was used to refer to a number of criminal gangs in New York City as well as Philadelphia.

The Baltimore Know-Nothing riots of 1856 occurred in Baltimore, Maryland between September and November of that year. The Know-Nothing Party gained traction in Baltimore as native-born residents disliked the growing immigrant population. Local street gangs became divided on political grounds, with the Know-Nothing affiliated gangs clashing with gangs affiliated with the Democratic Party. The partisans were involved in widespread violence at the polls and across Baltimore during municipal and national elections that year.