MEMPHIS — The release of video footage showing Memphis police officers pummeling, kicking and pepper-spraying Tyre Nichols, a 29-year-old Black man, drew a swift avalanche of reaction from law enforcement officials, lawmakers from both parties, Black Lives Matter activists and many other people across the country.

Their message was a largely unified expression of horror and disgust. The footage, which city officials made public on Friday evening, captured how what the police had initially portrayed as a routine traffic stop on Jan. 7 was an eruption of violent force directed at Mr. Nichols, who died three days later.

Yet protesters in Memphis and around the country largely heeded days of pleas from Mr. Nichols’s family and others to remain peaceful. Several dozen marched in Memphis on Friday night, spilling onto an interstate highway and blocking a major bridge; another demonstration was scheduled for Saturday afternoon.

Demonstrators have assembled in Washington, D.C., Seattle, Detroit, Atlanta and in Times Square in Manhattan. Officials said minor acts of vandalism were committed during a protest outside the Los Angeles Police Department’s headquarters, which was blocked by police in riot gear.

“The video is all the horrific things that were described to us,” said Josh Spickler, the executive director of Just City, a civil rights organization in Memphis, referring to days of warnings from law enforcement officials and Mr. Nichols’s family about the contents of the footage.

City officials in Memphis decided soon after the incident to make the video public as a step toward transparency. Four separate clips, from police body cameras and a surveillance camera mounted on a utility pole, were shared online, adding up to nearly an hour of footage.

On Thursday, prosecutors announced that five Memphis police officers had been charged with second-degree murder in connection with Mr. Nichols’s death. Almost a week earlier, those same officers — Tadarrius Bean, Demetrius Haley, Emmitt Martin III, Desmond Mills Jr. and Justin Smith — had been fired from the Memphis Police Department after an internal investigation found they had used excessive force and failed to intervene or render aid, as the agency’s policy required them to do.

Lawyers for the officers have urged the community to avoid rushing to judgment. Blake Ballin, who represents Mr. Mills, said in a statement that the videos have “produced as many questions as they have answers.”

The Memphis Police Association, the union representing officers, said in a written statement that the organization condemns “mistreatment of ANY citizen nor ANY abuse of power.”

“We have faith in the Criminal Justice System,” Lt. Essica Cage-Rosario, the union’s president, said. “That faith is what we will lean on in the coming days, weeks and months to ensure the totality of circumstances is revealed.”

After the video was released, Sheriff Floyd Bonner Jr. of Shelby County, which includes Memphis, said that two deputies who had appeared in the footage had been “relieved of duty” pending an investigation after he was concerned by what he saw. Separately, the Memphis Fire Department said that two of its employees were also being investigated for their actions at the scene.

Mr. Nichols was stopped on the evening of Jan. 7 as he was headed to the home he shared with his mother and stepfather in the southeastern corner of Memphis. Mr. Nichols, who was pulled out of his car by officers, can be heard on the video saying, “I’m just trying to go home.”

Mr. Nichols fled on foot, and when officers caught up to him, he was kicked, struck by a baton and pepper-sprayed, at one point screaming, “Mom! Mom! Mom!”

The officers, according to the video, escalated their use of physical force and gave conflicting orders, repeatedly demanding that Mr. Nichols show his hands, even as other officers held his arms behind his back while another punched him. After officers pepper sprayed and beat Mr. Nichols, they left him sitting on the ground unattended and handcuffed, and when medics arrived, they stood by for more than 16 minutes without administering treatment.

An independent autopsy commissioned by his family found that Mr. Nichols “suffered extensive bleeding caused by a severe beating,” according to preliminary findings.

As police departments around the country responded, law enforcement officials said actions shown in the video defied what officers are trained to do. “What I saw in that video was not right,” said Deputy Chief Gerald Woodyard of the Los Angeles Police Department, who is the commanding officer for South Los Angeles. “What’s going on in their minds, I have no idea.”

Chuck Wexler, executive director of the Police Executive Research Forum and an expert on law enforcement practices, called the officers’ actions “the definition of excessive force.” Ed Obayashi, a police training expert and lawyer who conducts investigations into the use of force, said the severity of what he saw in the video was alarming. “I’ve never seen an individual deliberately being propped up to be beaten,” he said.

Yet the video reflected something achingly familiar, as the country has grappled repeatedly with high-profile cases of Black men and women having fatal encounters with police, including George Floyd in Minneapolis and Breonna Taylor in Louisville.

“What I saw last night in that video shocked me to my core, but I can’t say I haven’t seen it before,” Gerald Griggs, the president of the Georgia N.A.A.C.P., said at a rally in Atlanta.

The video was regarded by activists and others to be as much of an indictment of the country’s policing culture as of the individual officers in the footage. “It’s a norm at this point,” said Kori John, a teacher in Brooklyn. “Black men getting destroyed by the police force, by even Black police officers.”

Mr. Nichols’s family is calling for legislation requiring officers to intervene when they see colleagues using excessive force; they have also demanded that the Memphis Police Department disband the specialized team patrolling high-crime areas, known as the Scorpion unit, that the officers charged in Mr. Nichols’s death had been part of.

In Sacramento, where Mr. Nichols grew up before moving to Memphis, family members planned a candlelight vigil for Monday, and local authorities urged protesters to demonstrate peacefully. Mayor Darrell Steinberg said the video filled him with “anger, sorrow and revulsion,” Kathy Lester, the city’s police chief, called the actions of the Memphis officers “inhumane and inexcusable,” and the Sacramento County sheriff, Jim Cooper, said the “horrendous acts displayed by these few officers do not reflect the values of this office or law enforcement as a whole.”

In Memphis, for days before the video release, city officials, civic leaders and Mr. Nichols’s family beseeched the community not to allow protests to become destructive. The relatively quick criminal charges, which Mr. Nichols’s family applauded, may have helped head off conflagrations.

Even so, the anger and hurt were still there, leading some demonstrators to mobilize on Friday night and plan more protests in the coming days.

Hunter Dempster, an organizer with Decarcerate Memphis, a group pushing for accountability and fairness in the criminal justice system, said he and others were blocking the Interstate 55 bridge leading from Memphis into Arkansas because they were “tired of empty promises.”

“At the end of the day,” he said, “what recourse do we have?”

Many described watching the video as wrenching. “I can’t believe no one thought ‘we don’t have to keep beating this man.,’” Nino Brown, an organizer with the Party for Socialism and Liberation, said at a vigil for Mr. Nichols in Chicago.

Others, including Ms. John, the teacher in Brooklyn, had decided they would not watch it, saying that the burden of viewing that kind of trauma outweighed any benefit from watching it.

“I don’t want to see it — I can’t see it,” she said. “It’s so heartbreaking. We’ve seen that video so many times before.”

Reporting was contributed by Jesus Jiménez and Jessica Jaglois from Memphis; Robert Chiarito from Chicago; Shawn Hubler from Sacramento; Sean Keenan from Atlanta; Douglas Morino from Los Angeles; and Neelam Bohra, Hurubie Meko and Wesley Parnell from New York. Mike Ives also contributed reporting.