A teenager was airlifted to hospital after he suffered serious injuries at a skatepark in Wakefield.
The incident happened while the 17-year-old was riding his bike on equipment in Thornes Park at 2pm on Sunday.
He was taken by air ambulance to Leeds General Infirmary after sustaining the head injury.
Police said his injuries are serious but not believed to be life threatening.
Det Insp Vanessa Rolfe, from Wakefield District CID, said: “Early indications are that the incident appears to have been an accident but we would like to hear from anyone who saw what happened.
“We have notified the council who will be conducting an investigation into the circumstances and the skatepark will remain closed while that is carried out.”
Anyone who saw the incident should contact Wakefield District CID on 101, quoting log number 909 of July 3.