A teenager was "permanently scarred" after an attack at Glasgow's Kelvingrove Park.
The incident was one of many in the park on Friday when hundreds of people flocked to the area to enjoy the good weather.
The 16-year-old boy was at the entrance of Kelvin Way with a 16-year-old girl at 20:00 when a group of teenagers approached.
One of the group attacked the couple and the boy had a number of facial injuries.
He was treated at the Queen Elizabeth University Hospital of the city.
The police asked for information about a boy on the bike who was involved in the exchange.
It is described as about 15 years old, about 5 feet 5 inches tall, slender, and has short, shaved blond hair.
He was wearing shorts and a T-shirt and riding a black BMX bike. The officers also look for the other members of the group who were with him.
Det Con Stephen Palmer said: "This attack has left a teenager with a serious injury, who will make him forever scarred, violence is not tolerated in our communities, and it is very important that we find the person responsible for it.
"At this point, we do not know exactly why this altercation has taken place, and we urge anyone who knows anything about it to contact the police.
"There is a playground nearby where the incident took place, which people used then, someone must have seen something."
Four people were arrested and two more were taken to the hospital for outbreaks and concussions when riots broke out in the park on Friday afternoon.
According to the police, four young people, including a 17-year-old boy, a boy and a girl aged 15 and a 14-year-old boy, were arrested and charged with public order offenses.
The 17-year-old boy was also charged with assault.
Police were summoned to Kelvingrove Park, Glasgow city center, around 4:30 pm Friday after riots broke out among youth groups.
Photos in social media showed police vehicles and horses.