Around 20 youths were involved in scenes of disorder on a residential street in Leeds this weekend.
The trouble began after officers attended reports of a disturbance in Hawthorne Avenue in Yeadon on Saturday night.
One of those officers was injured and what was described as 'spontaneous disorder' involving a large group of people broke out.
Since then, it has emerged that an assault may have taken place on the street before officers first arrived.
The Leeds Outer West policing team issued a statement via its Facebook page on Sunday evening to explain the previous night's events.
Sergeant Chris Brumfitt wrote: "Last night [Saturday] officers attended reports of an ongoing disturbance on Hawthorne Avenue in Yeadon.
"Whilst officers were dealing with this incident a police sergeant was assaulted, sustaining injuries that required medical attention.
"Following this there was some spontaneous disorder involving approximately 20 youths and a number of arrests were made.
"Today [Sunday] I have spoken with a number of individuals present during this incident and parents of some those involved.
"They have all raised concerns over an assault that has allegedly taken place prior to police attendance.
"I can confirm that we have received a report of an assault having taken place at an address on Hawthorne Avenue and that this is currently under investigation."