A man was punched in the face and robbed of his phone on when he pulled his car to the side of the road to let another driver pass.
Det Insp Steph Wiseman, of Kirklees CID, said the man parked at the side of the road in Trinity Street, Batley, to let a car past when a man approached him and demanded money.
It was alleged that the driver was hit in the face repeatedly and property, including a mobile phone, was snatched from his car.
A man has been arrested in connection with the robbery but Det Insp Wiseman said the investigation was still at an early stage.
Anyone with information should call 101.