CNN  — 

Seattle police arrested at least 47 people Saturday evening in demonstrations against police violence and the presence of federal law enforcement in cities like Portland, Oregon.

At least 45 people have been arrested on charges of assaulting officers, obstruction and failure to disperse, police said. Twenty-one officers have been injured from having projectiles thrown at them, according to police. Most officers were able to return to duty, the department’s Twitter said. One officer was hospitalized with a leg injury caused by an explosive.

Police described the protest as a riot.

Seattle has been the scene of protests over police brutality and systemic racism, including in a six-block area controlled by protesters after police abandoned their precinct – the Capitol Hill Organized Protest or Capital Hill Autonomous Zone.

The zone known as the CHOP was started by demonstrators calling for justice in the death of George Floyd. But the demonstration devolved over time, and after a series of shootings, police cleared the zone on July 1. As CNN wrote at the time, CHOP’s failure was a case study in human nature, violence, mental illness, homelessness, and the difficulty in imagining a world without police.

Police cleared the zone on July 1. Three days later, a protester was killed during a demonstration.

CNN’s Samantha Guff, Jennifer Henderson, Madeline Holcombe and Elle Reeve contributed to this report.