The altercation took place on the westbound carriageway between Langrish and West Meon at about 4.30pm, on Wednesday, December 14.
The 46-year-old male victim was driving a silver Vauxhall Astra when he noticed a white Ford Transit van behind him. The van overtook the Astra and slowed so that both vehicles stopped.
The van driver got a metal scaffolding pole from his van and used it to smash the victim’s window and wing mirror.
The van driver was wearing a hooded top and is described as white, around 5ft 8ins tall, in his late 30s to early 40s, of stocky build, and with a crew cut hair style. Anyone with information should call 101, quoting 44160471251.
Alternatively, people can call Crimestoppers on 0800 555 111, where information can be left anonymously.