Police say the 64-year old man was walking on Prospect Street during his lunch break Tuesday when the four came up behind him, punched him in the face, then picked him up and slammed him to the ground.
The man suffered multiple fractures to his neck, back and left arm.
He is being treated at Stamford Hospital where he will have to undergo surgery.
Through surveillance video and the account of one witness, police identified and arrested one of the suspects, a 15-year old Bridgeport resident who attends Stamford Academy.
Police say the witness confronted the teenager a short time after the attack.
Investigators are trying to identify the other suspects, and ask anyone who witnessed the attack to notify Stamford Police at 203-977-4417.