Officers Robert McCabe and Aaron Torgalski were suspended by Buffalo Police State Department after footage of the incident in the city on Thursday evening went viral.

The pair pleaded not guilty to the charges on Saturday, as a large crowd of fellow police officers and firefighters stood outside the city court to show their support for them.

Earlier, all 57 members of a tactical unit at the police department resigned from the team in protest at the suspensions, with Buffalo Police Benevolent Association President John Evans saying they were simply “following orders”.

“Our position is these officers were simply following orders from Deputy Police Commissioner Joseph Gramaglia to clear the square,” he told The Buffalo News.

“It doesn’t specify clear the square of men, 50 and under or 15 to 40. They were simply doing their job. I don’t know how much contact was made. He did slip in my estimation. He fell backwards.”

Speaking to local TV station WGRZ, he said the team had quit the unit “in disgust because of the treatment of two of their members, who were simply executing orders”.

He said the 57 remain police officers, despite having stepped down from the unit.

Footage of the incident emerged as protests over the killing of George Floyd continued across the US.

The video shows the elderly man approaching a line of officers wearing riot gear. One officer pushes the man with a baton before a second man shoves him.

The sound of a crack is heard as the man falls backwards and hits the ground and blood trickles from his head.

Most of the officers march past after the man falls. The officer who pushed him with a baton initially leans over him before he is motioned away by a colleague.

Buffalo Mayor Byron Brown said the man was in stable but serious condition in hospital.

He said Police Commissioner Byron Lockwood ordered an investigation and suspended the two officers after seeing the video.

“I was deeply disturbed by the video,” the mayor said in a statement.