Hundreds of people belonging to 'a variety of groups with various ideologies' gathered in the street on the Southwest 3rd Avenue side of the Justice Centre and in the nearby park.
Several sporadic brawls erupted between them, with projectiles and fireworks being thrown and pepper aerosols and bear spray being put to use.
People battled each other with bats and sticks, with some of them wearing protective body armor and gas masks.
"While the activity in the group met the definition of a riot, PPB did not declare one because there were not adequate police resources available to address such a declaration", local police said in a press release.
Before 3 pm, one of the groups left while others regrouped and returned to the area of Terry Schrunk Plaza. Later, the police declared "an unlawful assembly" in the park and ordered people to disperse.
On Saturday morning, police declared "an unlawful assembly" and arrested nine people after the Friday match after “heavy damage to police cars and injuries to officers” was inflicted.
Protests against police brutality and racism have erupted in Portland and other US cities after the death of Minnesota resident man George Floyd in police custody on 25 May. The Portland protests have since evolved into a nightly battle against the federal forces that President Donald Trump deployed to the city to get the situation under control.