On June 18, 1850, in Cincinnati, one constable was killed and one seriously wounded by John C. Walker, wielding a bowie knife, in a case that set a precedent for self-defense law.
Walker, a slightly built Ohio Medical College student, had gone to a show at the Van Amburg's Circus, getting there early so he would be able to stand at the front. Two off-duty city watchmen, Peter Davison [or Davidson] and Alexander Dalzell, had been hired by the circus to keep order. They wore no uniforms or badges. When the tent was nearly full, Dalzell went to the front of the crowd and ordered everyone to stand back. When Walker didn't move, Dalzell violently shoved him back about ten feet. Walker protested and moved his hand toward the breast pocket of his coat. Seeing this, Dalzell threatened to kill him if he pulled a knife, and then punched him in the face, knocking him down. Dalzell then jumped on Walker and held him against the ground as Davison came up and grabbed him with one hand while his other held an upraised cane. Walker drew a bowie knife and stabbed each of them. Davison hit him on the head with his cane, but whether this happened before or after he was stabbed is not clear.
Walker got to his feet and called for a policeman, and when one arrived, he surrendered his knife. The knife had been given to him by a friend when he had been considering enlisting for the Mexican War, and he had been advised to carry it for protection when he was in Cincinnati.
Davison died of his wound a week later, but Dalzell recovered after lingering near death for weeks.
Walker was tried for murder. However, as Dalzell and Davison were in private hire and had attacked Walker without provocation, he was acquitted on the grounds of self-defense.
A detailed account of the case is given in Reports of Cases Argued and Determined in Ohio Courts of Record, Volume 1.