A New York police officer told a court on Monday that an Occupy Wall Street activist left him dazed and in pain by elbowing him in the face as he led her away from a protest.

Testifying at Manhattan criminal court, Officer Grantley Bovell said that Cecily McMillan struck him after complaining about being made to leave Zuccotti Park on the night of 17 March 2012. She was shouting to people nearby who were holding cameras and mobile phones, he said.

"As I'm walking her out, I remember her yelling 'are you filming this?' 'are you filming this?'," said Bovell. "I'm like: 'filming what? So I decided to look and see what she was talking about ... I remember the defendant crouching down and, all of a sudden, she lunged her elbow back and hit me in the face".

McMillan, 25, is accused of assaulting Bovell, 35, and trying to stop him performing his duties during an operation to clear the park of hundreds of people who had gathered to mark six months of the Occupy movement. She denies the felony charge and faces up to seven years in prison if convicted.

Bovell, a Barbados-born US Navy veteran of the 40th precinct in the south Bronx, said that he first encountered McMillan "screaming at a female cop" after the crowd in the lower Manhattan park were told by a senior officer with a bullhorn after 11.30pm that they must leave so that the site could be cleaned.

"She was screaming that she shouldn't be forced to leave, that she shouldn't have to leave," Bovell said, under questioning by assistant district attorney Erin Choi. The officer, who said that he was wearing full uniform, said he told McMillan during a five-minute face-to-face conversation that she and everyone else were welcome to return to the park once it had been cleaned.

"The young lady said she didn't want to go. I placed my hand on her shoulder and I was walking her out of the park," said Bovell, who added that McMillan complained that the situation was "not fair" and "bullshit". The officer said his "open-palm" left hand was on McMillan's right shoulder.

"She struck me in my left eye - the left side of my face," said Bovell. "I felt a sharp pain. I remember it was like black, blue and white, and that I had a minor headache at the time". He went on: "It happened so fast. My glasses were all twisted."

Bovell said that McMillan immediately attempted to flee, but fell down on to her front with one of her arms trapped underneath her. He tried to grab her and then fell on to her back, he said, and began handcuffing her with plastic cuffs.

Sergeant Joseph Diaz, of the Manhattan South Task Force, told the court on Monday that he saw McMillan sitting in handcuffs on the pavement. "I think she was having a hard time breathing, or having some kind of distress," said Diaz. "It looked like she was having some kind of difficulty".

One of McMillan's attorneys, Rebecca Heinegg, told the court in her opening argument last Friday that McMillan did not intentionally strike Bovell but simply "reacted in surprise" to being grabbed from behind on her right breast. A photograph of McMillan two days later previously released by her supporters shows a bruise in the shape of a hand on her chest.

"As she reacted, she hit Officer Bovell in the face with her elbow," said Heinegg. "She did not intend to hurt him, she certainly did not intend to prevent him from completing his police duties. She did not even know that the person grabbing her from behind was a police officer. She just reacted. And ladies and gentlemen, reacting to being grabbed by a stranger is not a crime".

Judge Ronald Zweibel reacted furiously on Monday morning when about half a dozen McMillan supporters entered the courtroom wearing pink paper hearts on the right side of their chests.

"If anyone comes in wearing something like that on their chest, they are going to be ordered out of the building and not allowed back," Zweibel said, after ordering the jury out for a brief recess. A court police officer collected all the paper hearts. "You can have them back at the end of the day if you wish," he said.

Heinegg said in her opening on Friday that McMillan was a "committed" activist who was "known among other activists for her commitment to non-violence", but was in fact on "a day off from Occupy" on 17 March. She had been celebrating Saint Patrick's Day with a friend, said Heinegg, and stopped at the park briefly to collect another friend when the clash with Bovell took place.

The trial was adjourned for the beginning of Passover and is scheduled to resume on Wednesday morning. Zweibel has said that he expects it to last for three weeks.