A driver who stopped at a junction was punched repeatedly in the face by a pedestrian through the open car window.
The woman had stopped her car at Goldings Way in Braintree, near the junction with London Road, to give way to other drivers when the man walked by and hit her.
Paramedics were called and checked the driver, who is her 40s and from the Braintree area.
She was badly shaken and had bumps and bruises.
The incident was at about 4.30pm on Tuesday, May 20 but police have been unable to trace the attacker.
PC Daniel Smith said: "This was an unprovoked assault by a man who walked across the road and punched the woman when she stopped at the junction.
“She was punched about nine times and at one point pulled by the hair.
"This happened in a busy residential area and we hope that local people or other drivers might have seen this man in the area at the time.”
The man was white, thought to be aged in his 30s, about 5ft 10in tall and slim.
He had long brown hair and a beard and wore a a dark-coloured polo shirt and combat trousers.
Call Mr Smith at Braintree Police Station on 101 or Crimestoppers on 0800 555111.