A man whose skull was fractured after he was shoved to the ground by police officers at a protest in Buffalo last year has filed a lawsuit against the city and members of its police force.

The man, Martin Gugino, 76, claims in the lawsuit that he was “forcibly assaulted” by the police at the protest, and that other officers walked by as he “lay unconscious on the sidewalk, blood pouring from his fractured skull.” The suit, filed on Monday in the U.S. District Court for the Western District of New York, also alleges that the defendants tried to conceal the assault.

The filing, which claims that Mr. Gugino’s constitutional rights were violated, was the latest development in an episode that was captured on video and widely shared on social media last year. It added outrage to a period of protests over police violence after the deaths of George Floyd in Minneapolis and Breonna Taylor in Louisville, Ky.

One video captured by a local radio station shows two officers pushing Mr. Gugino, causing him to stagger backward and land hard on the sidewalk. Blood can be seen pooling beneath his head. The Buffalo Police Department said at the time that he “tripped and fell” during a “skirmish” after an 8 p.m. curfew.

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Richard P. Weisbeck, one of the lawyers who filed the lawsuit, said in a statement on Monday that Mr. Gugino had a constitutionally protected right to be at the protest in Niagara Square, Buffalo’s center of government. Instead, Mr. Gugino “became the victim of police brutality at the very moment he was peaceably and constitutionally protesting against police brutality,” Mr. Weisbeck said.

The lawsuit names Officers Robert McCabe, Aaron Torgalski and John Losi as defendants, as well as Police Commissioner Byron C. Lockwood and the deputy commissioner, Joseph Gramaglia.

Mayor Byron W. Brown, who ordered the curfew and said on his Facebook page on June 4 that Mr. Gugino had been involved in a “physical altercation” when he was “knocked down,” was also named as a defendant.

Michael DeGeorge, a spokesman for the city of Buffalo, said in an email on Tuesday that the city did not comment on pending litigation.

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