The panel ruled on Wednesday that former West Midlands Police officer Jack Green would have been dismissed, if he was still serving, for punching the man, who was detained for a mental health assessment, in October 2022.
The hearing followed an investigation by the Independent Office for Police Conduct (IOPC).
PC Green was accused of using excessive force on the man and speaking to him in a derogatory, disrespectful and discourteous way during the incident at New Cross Hospital in Wolverhampton on 30 October 2020.
Evidence gathered by IOPC investigators included police body worn video which showed that the former officer struck the man in the face and hip while he was restrained in a hospital bed with ankle and knee straps, handcuffed and with a spithood placed over his head.
During verbal exchanges with the man, PC Green told him that his breath stank, described him as "simple minded" and "pond scum", and said: “…you take too many drugs or drink too much booze, or just generally p*** your life away.”
The IOPC’s investigation began following a referral in February 2021 from West Midlands Police about PC Green’s conduct.
It took two months to complete and concluded that there was a case to answer for gross misconduct against the officer, who resigned from the force in May last year.
A three-day disciplinary hearing organised by the force and led by an independent and legally qualified chair found the allegations were proven.
It was determined that the former officer had breached police standards of professional behaviour for use of force and for authority, respect and courtesy.
IOPC Regional Director Derrick Campbell said: “Police officers must use only the minimum amount of force necessary to achieve the required result.
"In our view, the strikes delivered by PC Green were not necessary, reasonable or proportionate in the circumstances, and body worn video did not support his account that he acted in self defence.
"Police should also act with self control and tolerance but the officer did not provide a convincing reason for the way he spoke to the detainee.
“A gross misconduct hearing has now determined that ex-PC Green would have been dismissed if he had not resigned.
"He will also be added to the police barred list, preventing him from future employment with the service.”
At the end of the investigation, a file was passed to the Crown Prosecution Service which authorised a charge of assault against the officer, although the charge was subsequently withdrawn.
Following a separate conduct referral from West Midlands Police in March 2021, an investigation was started into allegations that two constables who were with PC Green during the incident had failed to challenge his behaviour.
On completion of the investigation in July 2021, it was found that both officers had a case to answer for misconduct for a potential breach of the police standards for challenging and reporting improper behaviour.
This was dealt with by the force through the Reflective Practice Review Process, involving the officers discussing with a senior officer the issues raised by the incident, in order to improve and learn for the future.