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."
True. The whole story is that the copper lost his rag and punched him viciously and repeatedly.
CCTV shows police punching park stab victim.
The footage, which was captured on council cameras, shows him being pinned to the ground and punched in the face.
True. The whole story is that the copper lost his rag and punched him viciously and repeatedly.