An 18-year-old Nottinghamshire man suffered serious head injuries when he was attacked in his parked car.
The man was in his red Peugeot 106 with a friend in a car park of Wingfield Avenue in Worksop when a large group of youths on bikes surrounded the car.
One of the group smashed the driver's window and the man suffered a blow to the head. He was shaken and drove off.
The man collided with a parked car and the Peugeot caught fire but he and his passenger managed to get out.
He was taken to the Royal Hallamshire Hospital in Sheffield where he was found to have bleeding on the brain. Police said the 18-year-old was now recovering at home after the attack on 17 October.
Pc Joanne Hall, from Nottinghamshire Police, said: "I am sure there are a number of witnesses to this attack who we have not yet spoken to.
"There were a lot of people around the car at the time and it is likely many of the residents in the surrounding properties would have seen something."
A 17-year-old man was arrested in connection with the attack but has been bailed pending further inquiries.
The attacker is thought to be aged 16 or 17, about 5ft 6in tall, of large build and was wearing a dark baseball cap, dark coat and dark tracksuit bottoms.
Anyone with information about the incident should contact police.