The Detroit News: Police: Off-duty officer shoots way out of holdup
Reading the article you can see he fired "at least ten rounds" which likely means more than that. If he was carrying the Detroit Police Department issued M&P 40, that would be 15 in the magazine and one in the chamber for potentially 16.
So much for the argument that no one would possibly need more than 10 rounds in a magazine, or that 10 is a magical "common-sense", "reasonable" limit.
While some may argue "But he was a police officer", He was off duty and acting completely as a law-abiding citizen when he was waylaid by the two individuals, at least one of whom had a rifle. Ten plus rounds were needed to protect himself, and fortunately he had that and lives in a state without an arbitrary and capricious magazine capacity limit.
He hit at least one of the two in the encounter, and that one was caught when he showed up to a hospital. The officer got out of the attack unhurt, so that counts as a win for the good guys.