Police are investigating an incident captured on CCTV which appears to show its officers punching a man who had been stabbed in a Liverpool park.
Darren Grace, 31, was found suffering head injuries and stumbling around Stanley Park on 1 August.
Merseyside Police said when officers tried to treat his wounds he became violent towards them.
The footage, which was captured on council cameras, shows him being pinned to the ground and punched in the face.
Supt Mike Shaw, from Merseyside Police's professional standards department, said he understood how people may be concerned when watching the footage.
However, he said CCTV images "never show the whole story."
Supt Shaw said officers were called to reports a man had been stabbed on Butterfield Street in Anfield at 0745 BST.
He said their inquiries had led them to Stanley Park, where they found Mr Grace with head injuries.
"During the course of administering medical assistance to Mr Grace he became violent towards the officers," he said.
"In this case, I understand that members of the public will be concerned when watching this footage.
"However, I would like to stress that CCTV images can never show the whole story."
He added: "As a police force we expect the highest standards from our officers.
"Where those standards are found to be breached disciplinary action is taken."
The force voluntarily referred the incident to the Independent Police Complaints Commission, which said it was happy for Merseyside Police to conduct its own investigation.
The professional standards department is carrying out the internal investigation.