Two men with scarves around their faces and brandishing a kitchen knife robbed three teenage boys in a Northampton park.
The youngsters were sitting on the benches of the basketball courts at the back of Bondfield Avenue when they were approached by two men, in their late teens or early twenties.
The men threatened the three victims with a kitchen knife and demanded they hand over their mobile phones and money.
One of the victims was then punched in the face several times and his phone was stolen.
It happened on Thursday, June 21 between 9.30pm and 10.15pm.
One of the offenders is described as a white man, around 5ft 8 tall, wearing a grey hooded top and bottoms, black gloves and a black scarf around his face.
The other offender is described as a white man, wearing black gloves and a black scarf around his face.
Witnesses to this incident, or anyone with information, should call Northamptonshire Police on 101 - alternatively, information can be given anonymously to Crimestoppers on 0800 555 111.