Montreal police say they arrested one woman and seven men on charges ranging from uttering death threats, assault with a weapon, obstructing police and intimidation.
Police also say several people were injured when they fell while running and at least one was taken to hospital.
About 100 people took part in the march, which was organized to protest government austerity, police brutality and capitalism.
The demonstration was quickly declared illegal because organizers had not provided a route to police beforehand.
Police say the protesters also smashed police car windows.
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