A 64-year-old man from Faringdon was arrested on suspicion of assault with injury and released under investigation.
The incident happened at around 3.30pm on Thursday (9/5) following a crash between two cars driving through the 50mph zone of the A34 near Botley.
A white Mitsubishi Outlander and a blue Toyota CHR both turned off northbound at the Botley Interchange before colliding with one another.
The driver of the Mitsubishi then got out of his car and kicked the Toyota driver in the stomach and head butted him.
The victim, a 53-year-old man, sustained bruises and a cut to his lip, but did not need hospital treatment.
Investigating officer PC Mark Russell based at Didcot police station said: "I am appealing for anybody that was in the vicinity of the A34 slip road on Thursday afternoon around the time of the altercation who believes that they witnessed the incident, to make contact with police.
"I believe that a number of people witnessed this incident as it occurred at a busy time of day.
"Witnesses are urged to call the 24-hour non-emergency number 101, quoting reference number 43190139158 or make a report online."
If you do not want to speak to the police, you can contact the independent charity Crimestoppers on 0800 555 111.