It was a logical conclusion to tzrider's post and bojangle's post that followed immediately after - that in general you want to train dogs using positive reinforcement, but in life or death training exercises sometimes negative reinforcement is required.
Couple that with bojangle's interpretation of the training exercise, where the dog was attacking and would not stop the attack when commanded to - that can easily result in a life or death scenario.
Pile on everyone saying "this is an assault on an officer" and my extrapolation of an officer using excessive force and not stopping when commanded to, bingo: punched officer.
Anyhow I don't really like advocating for punching dogs but I think bogangle and tzrider made excellent points about it while not tacitly endorsing it. Meanwhile I'm fully down for assaulting officers when an officer is about to kill someone.