Officers responded to reports of two men fighting in a parking lot at 893 Sir Francis Drake Blvd. at around 2:35 p.m., according to San Anselmo police.
Arriving officers contacted Novato resident William Hardsaw and another man who was bleeding profusely from a head wound.
Hardsaw told police that he and the victim had started a road rage argument driving west on Sir Francis Drake Boulevard, which continued when the two men pulled into the parking lot and got out of their vehicles.
The fight became physical, and when the victim grabbed Hardsaw's collar, he hit him twice over the head with a black flashlight.
The victim was taken to a hospital.
Hardsaw was arrested for felony assault with a deadly weapon and was booked at Marin County jail.