A security guard at an Upper West Side Apple store who saw the 2021 confrontation between an unruly man and an NYPD officer now indicted for assault said the cop “did nothing wrong” that day — and will testify on the officer’s behalf if necessary.

Brian Plunkett, 58, of Montrose, NY, told The Post that he still works at the store on Broadway where Officer Salvatore Provenzano struggled with the unidentified perp-turned-victim on Oct. 19, 2021.

But contrary to the portrait Manhattan prosecutors have painted, Plunkett said Provenzano acted reasonably when dealing with the man — who had allegedly pushed and threatened to stab the security guard before store employees called the cops.

“The police officers never touched him,” Plunkett said Thursday morning.

“The perp gave him an elbow to the side of the head, I don’t know if it connected. They put him on the ground and arrested him,” he continued.

“The cop is being railroaded.”

Plunkett added that he’d say the same thing before a judge.

“If I get called to court to testify, I will testify on behalf of the police,” Plunkett said. “He did nothing wrong.”

Provenzano had tried to remove the man from the store at about 9 p.m. that night, Assistant District Attorney Tavish DeAtley said at the cop’s Manhattan Supreme Court arraignment on Wednesday.

But the man — who neither police nor prosecutors have publicly identified — pulled away from him and headed for the door, DeAtley told the court. That’s when Provenzano allegedly slugged him on the left side of his face in an assault captured on bodycam footage, the ADA said.

“The people take seriously any incident where a member of law enforcement uses force without justification, and that is simply what we have here,” DeAtley told Acting Justice Maxwell Wiley.

A grand jury convened by the Manhattan District Attorney’s Office indicted Provenzano on a third-degree assault charge, which is punishable by up to a year in prison.

The officer — who has been stripped of his gun and is on desk duty over the charges — pleaded not guilty Wednesday.

He also rejected a plea deal that would have knocked the charge down to second-degree assault, which doesn’t carry jail time and won’t leave him with a criminal record.

It’s still not clear why it took two years to bring charges against him.

A spokesman said the DA’s office opened the investigation after it reviewed the body camera footage – but it would not elaborate on when that was.

“Our thorough investigation involved reviewing body worn camera footage and medical records and interviewing multiple witnesses,” DA’s office rep Doug Cohen said in a statement. “Yesterday, the defendant was arraigned on assault charges voted by a grand jury of New Yorkers and we are prepared to present our evidence at trial.”

The DA’s office didn’t comment on Plunkett’s claims.

Provenzano’s attorney, Stu London, said Wednesday he’s confident his client will be exonerated because his actions were justified.

On Thursday, London told The Post that he planned to call Plunkett to the stand when the case goes to trial.

“Isn’t that unbelievable that [the DA’s office] didn’t think it was important to call this witness?” London asked, referring to the grand jury proceedings. “I am grateful the media was able to corroborate what I indicated at the press conference: That this officer was justified in using minimal force of one punch.”

Plunkett said he didn’t press charges at the time because he didn’t want the attention. But he’s disappointed by the way the incident is being portrayed — and that the unruly man has been turned into the innocent victim.

“I was surprised when I saw on the news that this thing is still going on and that this poor cop is getting arrested for this,” Plunkett said.

“That’s what’s going on today, that’s the world,” he continued. “The police can’t be the police anymore, the police are the bad guys.

“That’s not the way the world should be.”