A 16-year-old boy was punched in the face by a passing motorist as he walked along Wood Street in Kettering, towards Bath Road.
The incident happened just before 8am on Tuesday, 24 May, when the driver of a car travelling in the direction of Rockingham Road stopped in front of him.
A police spokesman said: “A man got out of the vehicle and punched him, causing a bloodied nose and bruising around the left eye.
“The suspect then returned to his car and drove off.”
The attacker is described as white, 20 to 30-years-old, about 6ft with a muscular build.
He wore a grey hooded Converse top with the hood up, and drove a silver hatchback vehicle, possibly a Peugeot, described as having no exhaust and a noisy engine.
Witnesses or anyone with information about the attack can contact police on 101 or Crimestoppers anonymously on 0800 555111.