Yes, they can start by firing him.

James Frascatore, the New York City police officer who jumped and assaulted an innocent man, James Blake, in Manhattan last Wednesday, has disgraced the department. Commissioner William Bratton and Mayor Bill de Blasio should make an example of him. They should make it clear that his unprovoked aggression — caught by a security camera, so there is no doubt about what he did — reflects everything that causes people to distrust and hate the N.Y.P.D. The officer’s further transgressions — not identifying himself to Mr. Blake, not apologizing, failing to void the arrest in follow-up paperwork — speak to an appalling lack of judgment by someone unfit for the job.

The mayor and Mr. Bratton need to acknowledge all this, and they should explain a few other things.

Like: Why shouldn’t Officer Frascatore be arrested for assault? Why was he still loose on the street despite his long history of excessive-force complaints, first reported by WNYC, including punching a driver in the mouth (after stopping him for a broken taillight) and another man in the stomach (while calling him a racial slur)? That those victims were both black and Mr. Blake, is biracial deserves attention. Why is no action taken when multiple complaints are filed with the Civilian Complaint Review Board?

After the death of Eric Garner on Staten Island at the hands of the police in July 2014, Mr. Bratton promised to retrain all of his officers in professional, nonlethal arrest procedures. How could Officer Frascatore not have gotten the message?

Mr. Bratton fiercely defends his department’s aggressive policing of small infractions, so that “quality of life” in the city is preserved. But “quality of life” should also mean the freedom to stand on the sidewalk without worrying that a plainclothes officer will attack you.