Police have appealed for anyone with phone footage of a park attack that left a teenager with a head injury to come forward.
Hertfordshire Police said they were called to Gadebridge Park, Hemel Hempstead, just before 14:00 GMT, on Friday, to reports a 19-year-old male had been assaulted.
He was taken to hospital by ambulance.The force said it was “an altercation with a group of other males” that it believed were “known to each other”.
It said investigations were ongoing and asked any witnesses to come forward.
A police presence remains in the area, while inquiries are carried out.
“We are aware that there is phone footage of the incident in circulation and would appeal to anyone who has possession of this to contact us immediately”, it said.