Police are investigating after a posted video showed an officer punching a young woman in the face while responding to an incident at a St. Patrick's Day party in Chester, Pennsylvania, on Saturday.

Authorities were called to the scene of the party "for what was described to them as a riot" and found a group of people fighting in the street, police said.

A group of people attempted to go into the house and then tried to kick down the door when they were turned away, Chester police said.

Video of the brawl posted online showed one woman who raised her hand at an officer being punched in the face, according to NBC 10 Philadelphia. The officer who hit the young woman appeared to have his taser in his hand when he struck her.

The person who originally posted the video has since made their account private, and NBC News was unable to watch the recording in full.

Chester police said the woman in the video, Dominique Difiore, 20, struck a police sergeant and was arrested at the scene along with three other people.

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

Difiore made an initial court appearance on Sunday in regard to 20 criminal charges, including three counts of aggravated assault, one count of resisting arrest and one count of public drunkenness, according to court records.

Amanda Parker, Difiore's sister, said in a statement to NBC Philadelphia that her sister, "is doing as well as she can right now."

"My sister’s actions are questionable and she made a mistake," Parker said. "However, my sister is not a bad person. The officer involved is not a bad person."

Court records show Difiore was unable to post bail and was still in custody as of Monday afternoon.

A lawyer for Difiore did not immediately respond to a request for comment from NBC News.