Sixty-seven people were arrested during clashes between right-wing and anti-fascist protesters and police as a demonstration brought a town centre to a standstill.
Police condemned the violence in Bolton, Lancashire, during which protesters attacked police officers and injured members of the public.
Thousands of people took part in a rally in Victoria Square, organised by controversial right-wing group The English Defence League (EDL), which campaigns against "militant Islam".
Police said protesters from Unite Against Fascism (UAF), who organised a counter-demonstration, were responsible for most of the violence.
Of those arrested, at least 55 were from UAF and nine from the EDL, police said.
Assistant Chief Constable Garry Shewan, from Greater Manchester Police, who led the policing operation, said his officers faced "a lot of hostility" and "unwarranted attacks", resulting in injuries.
He said the EDL had protested by flag-waving and "vitriolic name-calling" but reserved his criticism for the UAF.
"Today in Bolton we have seen groups of people, predominantly associated with the UAF, engaging in violent confrontation. It is clear to me that a large number have attended with the sole intention of committing disorder and their actions have been wholly unacceptable.
"Turning their anger on to police officers, they acted with, at times, extreme violence and their actions led to injuries to police officers, protesters and members of the public.
"The police are not and should not be the target of such violence and anger, and this protest and the actions of some of the protesters is roundly condemned by GMP and by Bolton Council," he said.
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