No one has any requirement or obligation to physically fight someone already going after people with a deadly weapon, you simply just need to shoot them and stop the threat.
A cop is at work and can’t, and doesn’t need to fight everyone that you or I might if we were unarmed and a woman was being attacked, but they do need to be willing to do it when it is called for and appropriate, that is why city cops used to be required to be tall, large, male, and armed with a club, they couldn’t just shoot every person that could be perceived as a threat by a weak cowardly person in the wrong line of work, we wouldn’t have stood for it for one thing.