The 29-year-old policewoman hurt her arm while policing a cordon at the protest by the English Defence League in the city of Nottingham, but no one else was seriously hurt in the skirmishes, Nottinghamshire police said.
About 500 members of the EDL, a marginal group which has staged a number of demonstrations against radical Islam in recent months, sang the English national anthem and football songs as they gathered in the city.
Many of them had their faces covered with scarves and hooded tops as they chanted "`We want our country back" and held placards saying "Protect Women, No to Sharia (law)'' and "No Surrender''.
A counter-demonstration by Unite Against Fascism, which claims the EDL is a racist organisation, took place nearby, despite police requests that they move.