Watch This Protest Turn From Peaceful to Violent in 60 Seconds

On a mild June evening, a large but peaceful group of protesters supporting the Black Lives Matter movement marched toward the East Precinct police station house in the Capitol Hill neighborhood of Seattle.

Minutes later, the march ended in chaos as the police lobbed flash-bang grenades and sprayed the protesters with tear gas and pepper spray. Video of the clash, widely seen online, offers a lesson on how not to handle a crowd. But it also demonstrates a deeper problem in American policing: how officers often double down on a colleague’s decision, with potentially huge consequences.

The police have broad discretion in responding to protests that become unruly or block city streets. The judicious use of this discretion is critical to managing the crowd and protecting the First Amendment rights of protesters.

Before this march, which took place on June 1, the Seattle police and state troopers had set up barriers around the East Precinct station. Barricading areas around a station house is common during large protests. Officers need a place to park their personal cars, process arrests, eat, rest and use the bathroom. This is their base.

The marchers come to a stop at a line of metal barricades down the block from the station house. Bike officers are there to reinforce this line. They don’t appear threatening and the crowd doesn’t appear intent on breaching the barriers.

In the background, police officers in riot gear can be seen getting ready to deploy.

Soon, the bike officers are replaced by their counterparts in riot gear. The atmosphere becomes ominous. “We have a definite change in posture,” said Omari Salisbury, who recorded these images. “What we can expect next is tear gas.”

These riot officers wear combat helmets and gas masks, brandish batons and are equipped with pepper spray and tear gas.

Aggressive displays like this can send a message that the police expect to use force. Officers dressed for violence sometimes invite it.

Before using force against a crowd of protesters, officers should always warn them about what might happen if they don’t disperse, and give them an opportunity to comply. No warning is heard.

Noticing the arrival of riot police, some protesters open umbrellas to shield themselves from pepper spray.

A protester and an officer have a calm conversation. Further down the line, an officer bats away an umbrella that has been opened near his face. Blocking the line of sight — intentionally or not — can alarm officers. And in a tense situation with protesters and the police massed face-to-face, that can lead to an eruption.

The encounter turns violent when the officer yanks at the umbrella.

Officers nearby quickly blast the area with pepper spray. Perhaps they misread the skirmish as a sign that protesters were turning violent. Or perhaps they used it as a reason to break up the crowd with force.

To disperse a crowd, pepper spray should be aimed above people’s heads, but some officers here point it directly at protesters.

A sense of mutual commitment among the officers is on display. Seeing one of their colleagues reacting to a provocation with force, several officers start spraying indiscriminately at protesters.

Using force on the protesters seems arbitrary and excessive, but can be cast by the police as the start of a deliberate effort to scatter a threatening crowd. The reaction by that one officer may have committed the police to this logic of escalation. They send pepper spray deep into the crowd, and start throwing flash-bang grenades.

Tear gas soon follows.

Once the riot officers were in place on the line, they moved against the protesters in less than a minute, showing how quickly a simple altercation between a demonstrator and an officer can escalate unnecessarily.

What kind of emergency justified using pepper spray and tear gas against hundreds of people in what had been a loud but peaceful protest? Had the police patiently held the line until the protest naturally broke up, would this have happened?

This spot was the site of frequent protests. Days later, officers were still using force without warning, grabbing at umbrellas, deploying pepper spray and throwing flash-bangs. City officials questioned their judgment.

The mayor, the city council and a federal judge eventually prohibited the police from using tear gas against protesters. When the officers scaled back their response, the demonstrations, for the most part, broke up without intervention, showing what can happen when the police approach a situation intending to keep the peace.