A NSW police officer involved in the violent arrest of a disoriented and naked 16-year-old boy has told a hearing he feared for his safety as the "zombie-like" teenager advanced towards him.

The officer said weeks earlier he had dealt with a violent, drug-affected and naked young man with "exactly the same look" as the teenager had in the early hours of January 11 in a Byron Bay laneway.

Officer B was giving evidence in Sydney on Wednesday at the Law Enforcement Conduct Commission hearing investigating the conduct of officers involved in the apprehension, detention or treatment of the drug-affected teenager.

The unarmed youth suffered extensive bruising and a fractured rib in the incident.