WASHINGTON — Metro police arrested a man who they say threatened a Green Line train operator with a knife Friday morning for not moving the train fast enough.

Around 8:40 a.m., a Green Line train operator reported to police that he had been threatened with a knife by a man on the train.

The man, later identified as 29-year-old Norman Polk, kicked and banged on the door leading to the operator’s cab while it was stopped at the Anacostia Station, according a Metro police. When the train operator opened the door, Polk displayed a three-inch folding knife and threatened the operator for not moving the train fast enough, police said.

The Metro operator closed the door and radioed for assistance. There were no injuries, police said.

Metro police responded to the scene and arrested Polk on the Anacostia Station platform. Police recovered a knife at the scene.

The police activity caused a 15-minute delay on the Green Line during the morning rush hour.