The driver of the pickup, a 51-year-old Tumwater man, was believed to be under the influence of an unknown substance at the time of the crash, said Jen Kolb of the Tumwater Police Department.
The driver was arrested for investigation of vehicular assault, then released pending the results of the investigation.
Officers and medics responded to the scene, in the area of Linderson Way at Dennis Street SW, at about 8:45 p.m. after receiving a report of a vehicle hitting a pedestrian.
A 13-year-old Tumwater boy was found in the middle of the street with multiple serious injuries. It was reported the victim had been lying in the roadway prior to the collision, but it is unclear why he was there, Kolb said.
A preliminary investigation found that the boy was struck by 2007 GMC pickup being driven by a 51-year-0ld Tumwater man.
The driver was put through a series of field sobriety tests, which he failed. It is believed the driver was under the influence of an unknown substance, police said.
The victim was taken to St. Peter Hospital, where he underwent emergency surgery for multiple serious injuries.