A man was thrown to the ground and kicked by three teenage boys who demanded cigarettes and money from him.
The assault took place in Brooks Street East, Wellingborough, some time between 9pm and 9.30pm on Saturday, January 9.
The victim noticed the group of boys stood near to a small bridge which leads over the brook, into the Castle Fields Park.
As he walked past them they asked for cigarettes but he ignored them.
He noticed them following him so he stopped walking, at which point, they asked him again for cigarettes and this time money.
He was then dragged to the ground and kicked while they demanded money.
The group were disturbed by two passers-by.
Officers are keen to speak with these two key witnesses, who they believe may have been Polish men.
The first offender was white, 13 to 15 years old, tall and of medium build. He was wearing a blue or black hooded top with a grey hoodie underneath.
The second offender was white, 13 to 15 years old and of medium build. He was wearing a blue or black hooded top with a grey hoodie underneath and his face was covered by a dark fabric.
The third offender was 11 to 14 years old, slim and wearing a dark hooded jumper.
Anyone with any information can call Northamptonshire Police on 101.
Alternatively, they can call the independent charity Crimestoppers anonymously on 0800 555 111.