Nevertheless, it is clear that the rookie was poorly trained.
That danger is manufactured by the training received by the policeman. If you're in deadly danger from the police because you lawfully possess a firearm on your own property, well something ain't right. If the danger is real to an innocent citizen, then shooting the policeman who puts his hand on weapon approaches justifiable self defense.
It's up to the police to defuse the situation without it escalating into bloodshed, BTW. Good luck on that with the "shoot first" approach.