"This remains an active criminal investigation".
McGrier was detained but was not criminally charged in the incident, police said.
The city entered into a federal consent decree in 2017 after the U.S. Justice Department found officers routinely violated people's constitutional rights.
The latest incident happened at about 11:45 a.m. Saturday, when two officers encountered McGrier in east Baltimore.
According to WJZ-TV, the incident started when Williams asked McGrier for identification to fill out a citizens contact sheet, which Baltimore police are assigned to do after any interaction with residents. Williams' unnamed partner - who was placed on administrative duty - offered a half-hearted attempt to stop the assault.
The officer who struck McGrier has been a Baltimore police officer for just over one year, the department said. The agency has not released his name.
Attorney Warren Brown says his client, 26-year-old Dashawn McGrier, was hospitalized Saturday and not charged with any crime after Williams used him as a "punching bag".
Lt. Gene Ryan, president of the union that represents rank-and-file officers, had also said Saturday he believed Tuggle took "the appropriate action" by suspending the officer pending an investigation.
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According to Brown, McGrier is facing charges of assaulting Williams in June, which he denies. Brown said McGrier "may have suffered a broken jaw, a broken nose, maybe some fractured ribs, and he had difficulty with feeling his left leg, although before I left he did say that he was beginning to get the feel back in his foot, left foot".
Brown said McGrier was sitting on steps when Williams passed by in his vehicle, then moments later was walking down the street when the officer, now on foot, told him to stop without giving him a reason. In Baltimore's case, the agreement mandates changes in the most fundamental aspects of daily police work, including use of force, searches and arrests.
Baltimore Mayor Catherine Pugh called the video "very disturbing". "We are working day and night to bring about a new era of community-based, Constitutional policing and will not be deterred by this or any other instance that threatens our efforts to re-establish the trust of all citizens in the Baltimore Police Department".
Baltimore is still dealing with the aftermath of the 2015 death of Freddie Gray, who died in custody a week after a police encounter.
The consent decree also required the creation of an independent team of experts to monitor the police departments compliance.
"You see that video and you see what we are trying to prevent in the police department", said Scott, who is chair of the council's public safety committee. He was suspended shortly after the video first surfaced on Saturday. But Ryan added that there might be more to the incident that he does not yet know.
In February, while De Sousa was commissioner, a report raised questions about the qualification of Baltimores academy recruits.
Brown, McGriers defense attorney, said the beating "might be Exhibit 1 in that regard". Brown said he has scheduled a Monday news conference to discuss plans for filing a complaint against the officer.