A 16-year-old boy suffered head injuries after being assaulted by a man as he walked along a street in Paisley.
The incident happened at about 2130 BST on Friday on Netherhill Road, near to the junction of Dundonald Road.
The victim was taken to the Royal Alexandra Hospital where he was treated for his injuries.
Strathclyde Police are looking for a white man, aged about 25, of medium build and 5ft 10in tall. He was wearing a dark-coloured hooded zipper top.
He was also wearing a black baseball cap.
Officers say the suspect may have been accompanied by another man who did not take part in the attack.
Police would like to trace the man as they believe he may have vital information which could help their enquiries.
Det Con Gordon Gibson said: "This was a terrible attack on a young man who has been left badly injured and extremely distressed by the assault.
"It's unacceptable that anyone thinks they can randomly attack people on the street and I want to assure the community that we will use all resources at our disposal to trace the man responsible for this despicable attack."