A man was taken to hospital with head injuries after he was attacked outside a popular Halifax pub on Saturday evening.
The incident is believed to have taken place after both the victim and suspects had left Bow Legged With Brass on George Street.
Witnesses said that the victim had been attacked by a number of men.
A West Yorkshire Police spokesperson said: "Police are investigating a reported assault on a man on George Street, Halifax, at around 9pm on Saturday night.
"The victim reported being assaulted by a number of suspects and required hospital treatment for head and facial injuries. Enquiries are ongoing."