Asked by Richard Whittam QC, for the prosecution, what the officer was doing during the attack, Mr Brown said: "What I saw, he was trying to curl up into a ball, I suppose to protect himself somehow.
"Did he say anything?" Mr Whittam asked.
"I just heard heard screams of 'help, help, help'."
More top news
'Football sized' rubbish tip blight the lives of New Cross locals
Three security staff at a Vauxhall nightclub have been cleared of manslaughter after a man they restrained passed out and later died
A family is homeless after a fire in their tumble dryer. The family had been in touch with the manufacturer after a recall notice went out.