My opinion is that they waited too long to take care of the situation, and it nearly cost them an officer's life.
If an armed person is approaching an officer in a threatening way like that, they should take a limited amount of steps back before putting him down. They walked backwards for hundreds of feet, probably leaving their cruiser unlocked and possibly running in the driveway. What was stopping him from hopping in their car, or possibly accessing a weapon in there?
Lots of sloppy police work here.. the guy that ends up in the headlock.. Really?? Those are the abilities that your training has left you with?