Two police officers have been charged with secondary assault after a 75-year-old man was shoved to the floor, suffering a head injury.
Buffalo officers Aaron Torgalski and Robert McCabe are accused of assaulting peace activist Martin Gugino.
He was seen lying on the ground in a pool of blood in video which has been shared around the world.
Mr Gugino, from the city in New York state, is currently in a serious but stable condition.
Both officers pleaded not guilty to second-degree assault, and were released without bail.
Initially police said he had tripped and fell, but the clip, which has been viewed millions of times, shows him stumbling after being pushed.
When the two accused officers were suspended, all 57 members of Buffalo's Emergency Response Team quit in protest.
Large groups of colleagues turned up to show their support when the officers appeared in court today.
John Evans, president of the Buffalo Police Benevolent Association, said that officers were following instructions to clear the area.
He told the Buffalo News: “They were simply doing their job.
"I don’t know how much contact was made. He did slip in my estimation. He fell backwards."
Buffalo Mayor Byron Brown told reporters he has not asked for the officers to be fired.
"That investigation is proceeding - I've asked to move swiftly," Brown said.
"It is very important that the officers know they are getting due process."
"Our information was that individual was an agitator - he was trying to spark up the crowd," Brown said.
"What was reported to me was that individual was a major instigator."
