A protester used his head as a weapon to charge at and injure a policeman battling to keep rivals apart during a mass demonstration in Sunderland city centre, a court heard.
Thomas Allen, 58, has been fined and ordered to pay the officer compensation by magistrates who scolded him for his actions.
They were told the unprovoked attack caused the PC to tumble to the ground, causing grazing to an arm.
Despite the assault, he was able to keep hold of Allen, of Hartside Road, Pennywell, Sunderland, who was arrested.
Even Allen’s defence solicitor admitted his client was still “hyped up” when later questioned at a police station.
Sentencing Allen, who is believed to be jobless, magistrates in South Tyneside criticised him for being part of trouble which led to three arrests on the day.
They said police had better things to do than wrestle with a man of his age during what should have been an entirely peaceful protest.
The court heard Allen was part of two marches organised by left and right wing groups which descended on the city on Saturday, September 15.
One was by Wearside-based Justice for the Women and Children Group, which was joined by the Democratic Football Lads Alliance (DFLA).
A counter demonstration was held by Sunderland Unites and Stand Up To Racism North East, which included members of trade unions, political parties and politicians.
Trouble flared close to Keel Square when members of the DFLA ignored march stewards and tried to break through the police lines which separated them from the other group.
Prosecutor Lesley Burgess said: “The officer was in uniform and part of an incident ongoing in Sunderland city centre.
“He was keeping the peace between left and right wing activists. As part of the cordon, he was directing members of the protest.
“He instructed Mr Allen to continue on his way and in the direction of where the demonstration was a heading.
“Mr Allen took no notice. He ducked his head and charged at the officer into his stomach.
“The officer says that he had no regard for him and forced him to fall backwards, and they were both forced to the floor together.
“He kept hold of him and got a graze to his elbow.”
Harry Burn, defending, described Allen, who admitted one charge of assault when he appeared in court, as “hyped up” even after his arrest.
He said his client had denied the offence when interviewed, but admitted he might have pushed the policeman.
Mr Burn said: “It was not nice for the police officer. But the injury is what it is, it’s a graze to an arm.
“It’s not too serious. He hasn’t needed medical support, but it was his job and he didn’t need that to happen.
“Mr Allen apologises to the officer and to the court.”
Magistrates fined Allen £80 – reduced from £120 due to his guilty plea – and ordered him to pay £100 compensation to the officer.
He must also pay a £30 victim surcharge and £85 court costs, with the entire amount being paid at £10 a week.