A man was bottled and repeatedly stamped on at a house party in Earls Barton.
The incident happened at the party in Thorpe Road between 10pm and 11pm on Saturday, January 26.
A police spokesman said the victim was assaulted by a large group of black and mixed race men in their late teens to early 20s.
They said that during the attack, a bottle was smashed on his head and he was repeatedly stamped on, adding that he was taken to hospital where he received eight stitches to a head wound.
Anyone with any information should contact Northamptonshire Police on 101.
Information can also be submitted anonymously to Crimestoppers on 0800 555111.