A Byron Bay police officer who tasered a teenage boy and struck him with a baton at least 19 times should potentially be charged with assault and sacked, the state's police watchdog has found.
The Law Enforcement Conduct Commission, in a report presented to parliament on Thursday, said the officer used excessive force when he and three colleagues detained the naked and intoxicated 16-year-old in January 2018.
The commission suggested he could be prosecuted over the incident for assault occasioning actual bodily harm and sacked by the police commissioner.
The LECC in March held a public hearing to consider whether five officers involved in the boy's apprehension and detention engaged in criminal conduct or serious misconduct, after video footage of his violent arrest - in which he was also capsicum sprayed - aired on A Current Affair.
The boy, who was vacationing in Byron Bay with his family, told arresting officers "I'm not resisting" in the footage.
The LECC ultimately found that while four of the officers involved in arresting and detaining the teenager had not engaged in misconduct, the actions of the fifth - given the pseudonym Officer E - amounted to "serious misconduct warranting serious consequences".
"It is obvious that Officer E's intention was to beat (the boy) until he complied and, even when he was handcuffed, Officer E did not desist," the report said.
"No doubt he subjectively believed that he was entitled to do what he was doing but objectively he acted unreasonably and with grossly excessive force."
The officer's use of force was deliberate, unreasonable and "significantly beyond a mere error of judgment", the commission found.
The LECC accepted the officers attending the scene feared it could be similar to a recent incident involving a naked man, who smashed the window of a police car, and they felt he had to be restrained urgently.
While it was possible the teenager sustained a fractured rib before his arrest, the commission said it was most likely caused by Officer E.
The officer maintained throughout his questioning that the degree of force he used was necessary.
The commission released two other reports on Thursday.
One found that three police officers engaged in serious misconduct in the course of detaining a woman at a Sydney police station in April 2016.
The other suggested an officer engaged in serious misconduct when he punched an intoxicated woman in custody in September 2017 before sharing footage of the incident with other officers via Snapchat.
NSW Police said the police commissioner and commander of the professional standards command would consider the LECC recommendations.
Police Association of NSW president Tony King said drugs or alcohol were involved in each matter and they posed "significant and dangerous challenges" for officers.
"It is very simple in the cold light of day and with hindsight to judge the actions of our members but police officers make decisions in violent incidents in a split second," Mr King said in a statement to AAP.