Footage showing police holding down a teenage boy and hitting him with a baton has been played at an independent inquiry into the officers' conduct.

The Law Enforcement Conduct Commission (LECC) in Sydney is investigating whether the officers used excessive force and therefore engaged in serious misconduct while arresting the intoxicated 16-year-old in Byron Bay in January 2018.

The video, which runs for two minutes and 49 seconds, was filmed by a member of the public.

It shows four officers holding the teenager down, and one of the officers hitting him just under 20 times, with most of the blows coming from a baton.

The 16-year-old, who can only be referred to as 'AO', can be heard yelling, "Please help, help!" and then "I'm not resisting", while one of the officers can be heard saying, "Stop resisting, stop it".

In his opening address, counsel assisting the commission Terence Rowles said that police received a call from a member of the public at 2:00am on January 11 advising that a naked man was acting inappropriately in the vicinity of the Nomad's Backpackers Hostel in Byron Bay.

"AO was disorientated and appeared to be acting under the influence of drugs and/or alcohol," Mr Rowles said.

"Attempts to communicate with AO or to have him obey commands were unsuccessful, the police officers then used OC spray, a taser and finally physical force, including the use of batons, to restrain him."

Mr Rowles said AO suffered extensive bruising and a fractured rib.

"Although it is certainly the case that AO was acting irrationally and was plainly intoxicated in some way, he had not attempted to attack anyone, either physically or verbally, he was plainly unarmed," Mr Rowles told the commission.

"He was shouting, but to the extent that anything could be made out, he was not either swearing or threatening.

"One of the important questions that needs to be determined is whether, at any time, but more particularly before any physical interaction occurred between AO and the police, he attempted to attack any officer or acted as though he might do so."

'Reasonable suspicion of mental illness, intoxication'

All four police officers will give evidence and be cross-examined during the hearing, however their identities have been suppressed by the commission to protect their privacy.

"It is clear that when the four officers arrived they were faced with a difficult and unpleasant situation which certainly justified a reasonable suspicion of both mental illness and drug intoxication … and warranted immediate police intervention and removal of AO to a safe place," Mr Rowles said.

"How they went about this is task is the subject of this investigation."

The Law Enforcement Conduct Commission is an independent statutory body which is separate from the NSW Police.

Its role is to detect, investigate and expose serious misconduct and serious maladministration within the NSW Police Force and it has powers to protect persons who provide information to it.

Once this matter has been investigated, the commission will present a report to Parliament.