A police trainer has told a murder trial he would "never" train officers to restrain a person using their foot against their head.
Jurors previously heard PC Benjamin Monk was seen resting his boot on ex-footballer Dalian Atkinson's head as he lay incapacitated after being tasered.
The officer is charged with Mr Atkinson's murder during a stand-off in Telford, Shropshire, in 2016.
PC Monk, 43, denies murder and an alternative charge of manslaughter.
Mr Atkinson, who played for Aston Villa, Sheffield Wednesday and Ipswich Town during his career, died after PC Monk and co-accused PC Mary Ellen Bettley-Smith, 31, were called to his father's home on Meadow Close at about 01:30 BST on 15 August.
He was tasered for 33 seconds by PC Monk, who told jurors he was in fear of his life.
West Mercia PC Monk has admitted he kicked Mr Atkinson, but said it was not-targeted and "instinctive" however he challenged witness accounts that he then rested his boot on the sportsman's head.
Retired expert police trainer Ian Mills told jurors at Birmingham Crown Court pinning a subject's head was acceptable "but not with the foot".
"I've never trained it, I would never train it and I've never seen it," he said.
Mr Mills also said he would not train officers to kick subjects in the head, but when asked added: "There's no part of the body ruled out".
"There's just medical implications related to each part of the body and the tactics used on each part of the body," he said.
Mr Mills, who worked in policing for 28 years, wrote a report in which he said the job was "so diverse it'll never be possible to document guidance to cover every eventuality" and officers "must be prepared to account for their decisions" if they use alternative restraint techniques.
He also spoke about PC Monk's use of a Taser. The officer previously said he had no idea how long he fired the weapon for and Mr Mills said he had seen officers freeze in stressful situations and hold on to the trigger.
PC Bettley-Smith, 31, denies assault occasioning actual bodily harm.
The trial continues.