Two boys were attacked by three men who punched and kicked them in the face.
The teeangers, both 17, were walking along Earl Street towards Clare Street when they were approached by three men late on Saturday night (Apil 30).
The men shouted verbal abuse at the two boys before punching and kicking them in the face.
The offenders were all white, aged in their late teens to early 20s, around 5ft 10in to 5ft 11in, and casually dressed.
The assault happened between 11pm and midnight.
Witnesses, or anyone with information, are asked to contact Northamptonshire Police on 101.
Alternatively, they can call the independent charity Crimestoppers anonymously on 0800 555 111 or use the anonymous online form at www.crimestoppers-uk.org.