A video posted on YouTube shows the unidentified cop punching a woman in the face and knocking her to the ground before she is led off bloodied and handcuffed.
It was decided today that the officer would be placed on "restricted status," meaning that he is relegated to "administrative duties pending the outcome of the investigation," according to Lt. Ray Evers.
The video was taken at Sunday's Puerto Rican Day Parade, an event that Evers said "usually goes off without a hitch."
"We were made aware of the video very, very early this morning. Internal Affairs opened up an investigation in reference to the incident and the actions of that officer," Evers told ABCNews.com. "The incident is being fully investigated."
The video shows a crowd of blue-shirted police officers standing in the middle of a street, around a car. Someone on the left appears to throw something resembling silly string or a liquid on the cops. An officer in a white shirt rushes out of the crowd and goes after a woman with long, dark hair and a black T-shirt.
Her back is to the camera so it is unclear if she was saying anything to him. The officer appears to punch her in the face and then hit her in the back of the head. She falls to the ground where two officers apprehend her and lead her off. As she passes the camera, blood can be seen streaming down her face.
"The video speaks for itself," Evers said. "There were people in the crowd throwing items at the officer, water and other things."
The woman was taken into custody on a disorderly conduct charge and was later released. Evers said he believed she had a cut lip, but was not seriously injured.
Police are not releasing the name of the officer or of the woman.
The YouTube video, titled "Philadelphia Police Brutality" was posted on Sept. 30 and already has over 1,000 comments.
Some of the comments were in support of the officer, but the majority denounced his behavior.
"Regardless of what was done or provoked, the use of excessive force is apparent in this case. She was pursued and smacked, not restrained," one commenter wrote.
"She is obviously not [sic] threat and can easily be subdued by a man of his size versus her small frame plus there was plenty of back up," another wrote. "His position and authority contradict his actions, I would hope his rank was earned off of better judgement [sic] in the past because this was just shameful."