A driver in his 60s suffered serious injuries after he was "beaten around the head" in an alleged "road rage" incident.
Avon and Somerset Police said the motorist was "seriously assaulted" after two vehicles stopped on the A303 near the Sparkford roundabout at about 11:20 GMT on Saturday.
The man, who was driving a blue BMW, had to be airlifted to hospital.
His injuries are not thought to be life-threatening, the force said.
Police said the suspect - who was driving a grey Vauxhall Vivaro van - drove off towards Yeovil following the incident.
The A303 was closed for an hour as a result.