PITTSBURGH —The arrest of a 19-year-old woman who had a violent altercation with a Pittsburgh police officer during the annual PrideFest downtown on Sunday is under investigation by the city.

Ariel Lawther allegedly assaulted a police officer who was attempting to step in and break up a physical confrontation between her and a man on the street, according to the criminal complaint.

The incident happened in front of a crowd at Market and Sixth streets around 4 p.m. Mayor Bill Peduto said it started with an argument with anti-gay protesters. A small portion of what happened -- including footage of the officer punching the woman and grabbing her hair -- was recorded by a witness and posted on Facebook.

“She didn’t put up a fight, whatsoever. The only time she was throwing her hands up in the air is when he grabbed her by her throat,” said Jenna Kenny, who recorded the video.

The complaint says that Lawther, of Harmony, will face charges of aggravated assault, resisting arrest, simple assault and disorderly conduct. Peduto said he's withholding judgment until the investigation is complete, but he said the city "won't look the other way when incidents like this happen," and the arresting officer has been taken off the street during the investigation.