The incident took place at approximately 9.30pm on Friday 30 October outside the Tale of Spice restaurant on Castle Street.
The victim, an 18-yer-old man, was assaulted by a group of youths including being struck in the face with a bottle.
Police understand that someone from the Trowbridge Sports Bar, also on Castle Street, came out to the aid of the victim.
The victim was taken to the Royal Unit Hospital in Bath with a suspected fractured eye socket and released the following day.
Officers would appeal to anyone who was in this area of town at the time of the assault or has any further information on the attack to contact us immediately on 101 and quote crime reference number 54200109269.