Roger Cox denied assaulting PC Darren Calladine at the English Defence League and Unite Against Facism counter-demonstration on March 20.
But he was found guilty after a trial last month.
Howard Sloane, prosecuting, told magistrates how, on the day of the rally in Bolton town centre, PC Calladine was trying to arrest a man who was kicking out.
Cox and several other demonstrators pulled the man back into the crowd, with Cox hitting PC Calladine in the chest and swearing at him.
Cox, aged 29, of Croydon Road, Newcastle, was then forced to the ground by PC Calladine and a colleague, and was handcuffed.
Mr Sloane added that when arrested, Cox was found to be wearing football shin guards and when questioned at a police station declined to answer.
Andrew Fitzpatrick, defending, told magistrates that Cox has been approachable and cooperative with probation officers preparing a presentence report.
The court heard that Cox had three previous convictions in 2008 for possessing a knife, obstructing a police officer and a public order offence.
Yesterday, for the assault on PC Calladine, magistrates ordered him to do 250 hours’ unpaid work and pay £650 costs
