DeAndre Harris, a black man who was brutally beaten at a white supremacist rally in Charlottesville, Va., last year, was acquitted of assault related to an incident that took place moments before he was attacked.

Video from Aug. 12 showed six men surrounding Mr. Harris, 20, in a parking garage and hitting him with a metal pipe and wooden boards. Mr. Harris suffered a head wound and a broken wrist. The video was later widely circulated on social media in efforts to identify the assailants, and at least three men were arrested.

Moments before the attack, Mr. Harris had intervened in a scuffle after a friend tried to yank a Confederate flag away from a marcher, Harold Crews. A complaint by Mr. Crews, a state chairman of the neo-Confederate group League of the South, eventually led the Charlottesville Police Department to issue a warrant for Mr. Harris’s arrest, on a felony charge of malicious wounding. The charge was later amended to misdemeanor assault.