He said he had been a police officer for about two years before the incident, after being a farmer for many years.
He'd joined the force because he thought he could make a difference. The father of two adult children saw his role as being a peacemaker and mediator.
Mear said he did not condone the sort of behaviour he's alleged to have done.
Mear said allegations made by Constable Brian Newcombe, who told the court he saw Mear strike Mr Collier over the back of the head and "ram" his face into the ground, were a "complete and utter" lie.
In an interview, Mear told Detective Senior Sergeant Lindsay Pilbrow, the officer in charge of the case, that he smashed the passenger window of the car Mr Collier had been driving and that Mr Collier looked like he was "going" for a weapon. Mear said Mr Collier was trying to get away and it was extremely important to get him under control.
Mear told Mr Pilbrow he struck Mr Collier in a sideways motion with his torch at least twice, aiming for his hands. Mear said he knew the torch made contact with Mr Collier but didn't know where. He denied allegations of police brutality.
"I didn't join the police to hurt people. I joined the police to help."
Under cross-examination by Crown solicitor Greg Hollister-Jones, Mear denied "losing his cool" during the incident.
Another defence witness, Rotorua police officer Sergeant Colin Pears, told the court he had never seen Mear lose control.
Mr Pears, who is in charge of the Rotorua Tactical Crime Unit, said he had been in a number of situations with Mear.
"There's no one calmer than Dave [Mear] in my opinion."
Asked about Mear's honesty and integrity, Mr Pears said Mear was "as honest as the day is long".
The jury is expected to retire to consider its verdict today after closing addresses and Judge Phillip Cooper's summing up.