The department says it has a number of concerns regarding the violent tactics Officer Ian Walsh used.
Walsh stopped 17-year-old girl and her friend to cite them for jaywalking. A witness recorded video of the confrontation the ensued.
When Walsh tries to bring the girls to his patrol car, the situation appears to escalate. One girl can be heard yelling for the officer to get off of her.
The video shows the officer trying to grab the hands of the 19-year-old. But when the 17-year-old tries to break the officer's grip, he responds by punching her in the face.
Police arrested both girls, and the crowd can be heard reacting to the situation.
Department officials say their officers are trained to throw a punch in certain situations, and the department will withhold judgment until an investigation is complete.
Civil rights activists are outraged and say the punch was an action of anger not self defense.
The incident comes weeks after another high profile video surfaced showing Seattle police kicking a man they thought was a robbery suspect. He turned out to be the wrong person.