Police say William Mosson was booked on charges of assault with a deadly weapon after he cut off another driver, then jumped out of his car to beat the victim with a hammer.
The incident took place around 2 p.m. at Santa Teresa Boulevard and Chesbro Avenue.
Mosson allegedly cut off the victim, who made a "gesture" at Mosson, then both pulled off the road where Mosson produced a hammer and began beating the victim several times on his head and body, said Officer Jose Garcia.
The victim was taken to a hospital. Mosson is in custody on $40,000 bail.