By Matt Petrillo

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CHESTER, Pa. (CBS) – An out-of-control St. Patrick’s weekend celebration in Delaware County has several young adults facing charges and a police officer under fire. A viral video shows the cop striking a woman in her face, but police say that’s only half of the story.

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The cop can be seen hitting 20-year-old Domenique Difiore in the face. Police say the woman pushed the officer, and the video appears to support that theory. But some are questioning the amount of force the officer used.

Chaos erupted on East 15th Street on Saturday night, and it only seemed to worsen. Cellphone video captured a Chester police officer striking Difiore in the face and knocking her onto the ground. It happened after police were trying to take control of an apparent drunken brawl.

“It was just very hectic,” Zachary Whalen, a senior at Widener University, said. “I would say probably 30, 40 people were just running around here, just beating the crap out of each other.”

Sources told Eyewitness News that the brawl happened during a Widener University pub crawl.

The university said in a statement it was not a “university-sanctioned event.”

“An incident that led Chester police to arrest four individuals Saturday, March 16 on aggravated assault and other charges did not take place on the Widener University campus and was not a university-sanctioned event. The four people who were arrested are not Widener students. The matter is under investigation by Chester Police.”

Police arrested several people, but it’s the officer appearing to hit Difiore that has this typically quiet neighborhood clamoring.

“I was shocked,” witness Latine Bethea said. “I was really shocked. I couldn’t believe a man hit a female like that.”

Cameron Thomas, another witness, said Difiore fell instantly.

“He dove to the ground, then tased her,” Thomas said. “That’s what made it excessive.”

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“Granted, she did push the officer so as soon as you do that, I was like, ‘This is not going to be good,’” Whalen said.

Witnesses say after Difiore fell to the ground, the officer tased her ear.

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“Her whole ear was gushing blood,” said Jaylene Westfall, who was also arrested. “She was nonstop bleeding by the ear. She was in shock.”

Difiore was arrested along with Westfall, 19, and two others – Shawn Connelly, 21, and Tess Herman, 20. They were charged with aggravated assault and alcohol-related offenses.

“A partial video of the event is circulating on various social media platforms. The incident, the video and the level of force used in connection with the event are all currently under investigation,” Chester police said in a statement.

Still, to many people who live in the neighborhood, the video is clear.

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“I think it was excessive force,” Matt Pfaff, a neighbor, said. “I think it was ridiculous to do something like that, no matter how frustrated you get. They’re trained to do better.”

Chester police have not named the officer who struck the woman and did not say whether or not that officer is on leave.

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Her family told Eyewitness News that the officer should not have used such great force.