Surveillance video played in Manhattan court Friday showed the moment an ex-NYPD cop pummeled a cuffed, mentally ill man at a housing project.

In the footage, which has no audio, former Officer Elijah Saladeen can be seen struggling with Jeremy Santiago, then 19, near the Fulton Houses elevator banks on Feb. 24, 2017.

At one point, Saladeen, 49, stands over Santiago, who is on the ground, while the cop’s partner, Natalie Roman, shouts, “He’s about to bite you!” Roman testified Friday, filling in for the missing audio.

Saladeen then repeatedly punches Santiago on the side of the head, according to the video.

Roman tries to grab Saladeen’s arm to stop him from hitting Santiago, barking “That’s enough!” according to her testimony.

The video was introduced while Roman was on the stand on the first day of Saladeen’s assault and offering-a-false-instrument trial in Manhattan Supreme Court.

Another camera angle showed Saladeen dragging Santiago, still cuffed behind his back, to a rear hallway and slugging him repeatedly in the ribs.

“What the f–k are you doing?” Roman testified she shouted at Saladeen.

Santiago’s face was covered in blood and required stitches after the incident.

“The defendant brutally assaulted a defenseless, handcuffed Jeremy Santiago,” said Assistant DA Michael Mulanaphy in opening statements.

Before the incident, prosecutors said Santiago was sleeping on the 25th-floor stairwell landing after he had a fight with his brother, who lives in the building.

Saladeen and his partner roused Santiago, who suffers from bipolar and schizophrenia, then checked with his brother to confirm he wasn’t trespassing. But his brother, still annoyed from their spat, denied knowing who he was, prosecutors said.

Roman testified that Santiago grew increasingly agitated and slammed his head against the wall as he wailed, “I don’t want to go to jail!”

Saladeen cuffed him from behind, and the officers escorted him downstairs, where the fight occurred and Santiago was arrested. Prosecutors argued that Saladeen lied about the attack in written reports and to his supervisors.

Defense lawyer Craig Hayes countered that Saladeen acted in self-defense, slugging Santiago only after he had resisted arrest and tried to bite him.

“Police work at times will be ugly,” the lawyer said. “Just because something is unpleasant to view, doesn’t make it criminal.” He called the case “Monday-morning quarterbacking at its best.”

Hayes said Saladeen escorted Santiago to the rear hallway not to beat him up but to wait for an ambulance at a more accessible entrance.

The omissions and discrepancies in official paperwork were attributable to sloppiness, not an attempt to cover up his actions, the lawyer added to Justice Robert Mandelbaum.

Saladeen waived a jury trial, leaving his fate in the hands of the judge.

The housing cop was fired in September after an NYPD administrative hearing found him guilty of misconduct related to the incident. He will collect his pension.