Rammed and thrown by a car which broke his leg, at an incident with an active shooter, police officer B knew that the driver had to be stopped. He opened fire.
He told Coroner Sue Johnson of his instant decision at the inquest into the death of Donald Melville Ineson who was fatally shot by police in November 2018.
Police officer B told the third day of the hearing: "I just knew we had to stop him at that point. I knew I was pretty busted up. I felt my leg buckle up and I was pretty aware it was broken, and my left arm didn't seem to be working. It seemed to be numb and weak.
"I sat up and began shooting at Mr Ineson."
He fired several shots at the car which had struck him as it turned out of the driveway in Bangor Rd, near Darfield. He fired as it drove off down the road.
The car did a U-turn and came back towards officers A and B who had been called to an armed incident, but it pulled over to the side of the road and stopped. When police colleagues arrived, Ineson was found dead inside. He had been hit by a bullet fragment which struck him in the upper back and penetrated his chest.
The inquest was told on Monday that Ineson had armed himself with a shotgun after a dispute with his wife, and had fired two shots outside the house where she and her two children were sheltering.
He then smashed his way into the house using an axe, and took the car keys. In response to the wife's 111 call, two armed policemen arrived outside the property as Ineson was leaving in his car.
Officer B said the police said "time equals lives" in these circumstances. Their method was to go straight to the address and confront the offender regardless of back-up.
As they approached the address, they saw someone at the car in the driveway.
Officer B challenged him, shouting, "Stop, armed police."
Ineson carried on getting into his car 20m away. "He just floored it out towards us." The car would have reached 50km/h.
"I could tell he wasn't going to stop. I moved to the left further. I thought we absolutely have to stop this guy."
The car veered towards where he had moved, so he sprinted towards the right, but the car straightened up and hit him throwing him over the bonnet and through the air. "I felt it was deliberate. He changed direction from the way he was driving."
He said he fired because of the risk Ineson posed. The police did not know what had happened to his family - he was armed and had made threats and had fired shots. At the last update he was breaking into the house. "For all I knew his family was already dead inside."
"I could not allow him to escape. He was too much of a danger to the public and police members," said Officer B.
Both officers had fired at the car. Bullets were found in the car, and a fragment was recovered from Ineson's body but it was not possible to say which rifle had fired the fatal shot.
Officer B told how after being shot he had crawled through a ditch and hedge and then a householder offered to help him into his house. Instead, he asked to be helped to the gate where he lay sheltering beside some power poles to provide cover for his colleague who was still out on the road. They saw that Ineson had stopped his vehicle along the road.
The inquest is continuing.