A 17-year-old boy was assaulted in the alleyway off the Wellingborough Road by two masked men.
The teenager was walking in the alleyway, just past the Volunteer pub, which links St Edmund’s Road and Wellingborough Road when he noticed two men.
As he walked past them, they grabbed him and pinned him against the wall, and used what is believed to be a Stanley knife to scratch his face.
They also squirted an unknown liquid into his face from a Lucozade bottle which stung his eyes but caused no long-term damage.
After the assault, the offenders ran off towards Wellingborough Road.
They are described as wearing black tracksuits and trainers with black bandanas covering their faces. They spoke with Eastern European accents.
Witnesses, or anyone with information about the incident, which happened between 3.15pm and 4.15 pm on Tuesday, 16 August, are asked to contact Northamptonshire Police on 101. Alternatively, they can call independent charity Crimestoppers on 0800 555111.