PORTLAND, Ore. – A TriMet bus driver was assaulted during an argument over a fare with a rider early Monday morning, an agency spokeswoman said.

The driver was not seriously hurt.

The dispute started on a line 71 bus just before 6 a.m., according to TriMet spokeswoman Roberta Altstadt. A rider struck the driver in the face and left the bus. He was last seen walking eastbound on Southeast Powell Boulevard near 122nd Avenue.

Transit police are looking for a suspect who is white and between 15 and 18 years old. He is described as 5-foot-11, 175 pounds with longer brown hair. He was wearing a black hooded sweatshirt and blue jeans.