The Seattle Police Department asked WSP to investigate the Oct. 18 incident, which was captured on video.
The department said a plainclothes officer kicked a 17-year-old suspect during a drug bust in downtown Seattle.
The video shows an undercover officer attacking a suspect who has his hands raised.
That officer, James Lee, has been placed on leave. He is said to be a 10-year veteran of the force.
Five minority bar associations outrage by the footage have joined the American Civil Liberties Union to formally petition the Department of Justice to investigate a series of incidents involving the use of force by Seattle police.
The request asks the Justice Department's Civil Rights Division top determine whether these actions and others by Seattle police amount to a pattern of civil rights violations.
Seattle's Office of Professional Accountability has also launched its own investigation.