Police allege a group of men, believed to be of Pacific Islander apperance, approached the victim about 8pm and assaulted him on a city-bound train.
The victim ran off the train at Jannali and police were called.
One youth, was arrested at Mortdale train station and three others at Hurstville train station.
All four were released pending further inquries.
The man was taken to hospital with swelling to his jaws, eyes and face.
Source: The Leader