The NRI victim, Sanjay Jaiswal (35), who was admitted to the ICU of Nanavati Hospital, is in critical condition, police said.
The accused Indrajit Sawant (35), a manager in a private firm, has been arrested on the charge of attempt to murder and remanded in police custody till June 12.
According to police, on Wednesday evening, Rishi Gandhi, an executive with a private company, had gone to collect his Maruti car from a service centre in Kalina. As his car came out of the lane, it collided with a Chevrolet Optra being driven by Sawant.
Furious Sawant barged out of his car with a baseball bat and smashed windscreen of Maruti car before assaulting Gandhi.
Jaiswal, who was on evening walk, saw the commotion and tried to save Gandhi from being beaten up by Sawant. After a while, Sawant hit Jaiswal on his head with the baseball bat.
Seeing this, the onlookers got enraged and assaulted Sawant and smashed his car.
While Gandhi was discharged with minor injuries, Jaiswal, who was on a holiday here, is still battling for life.