The man stopped his spiked car in Te Teko. He pointed a shotgun toward police officers as he ran across the road to steal a BMW, parked outside a dairy.
An officer, believing the man was firing at himself and other officers, shot his Glock pistol at the man five times.
While the man sat in the driver's seat of the BMW, the officer fired three more shots, hitting the back of the car.
The man then appeared to be getting out of the car with his shotgun, and the officer fired one last shot.
The man dropped the shotgun onto the footpath before driving off in the BMW. He was taken into custody a few hours later.
The entire shooting incident took place over 37 seconds and the officer's nine shots were fired over about 15 seconds. No one was injured.
There is no evidence the man actually fired his shotgun. However, the authority believes it was reasonable for the officer to genuinely believe he was firing toward him and other officers, given an analysis of video footage of the incident and witness accounts.
The authority found the first five shots and the last shot fired by the officer were justified in order to defend himself and others.
Authority chair, Judge Colin Doherty, said: "I accept the officer's overall actions were to defend himself and others, in this fast-moving, challenging situation. However, it is implausible to believe he perceived the man posed an immediate threat to anyone while the man was sitting inside the car, at the instant the officer pulled the trigger to fire shots six, seven and eight."
The officer fired some of the shots from his slow-moving patrol car, a practice which is not currently addressed in policy. Police are amending the policy to ensure this is covered.
The authority also found police did not follow all procedures after the shooting incident.
Police said in a statement they acknowledged the findings of the authority.
Bay of Plenty District Commander Superintendent Tim Anderson says this was "a high-risk incident for our officers involved".
"This was an extremely dangerous incident.
"I am proud of the officers involved and how they reacted to a fluid and fast-changing situation. As always, we review these incidents and take learnings from them.
"I am grateful that no one was injured and that our officers were able to go home at the end of their shift.
"We have ensured they have been supported following this incident."