how is this justifiable?

[Purrrfect9]

Actually the lesser wolf willingly submits, they aren't physically forced. And dogs aren't wolves. Unfortunately "alpha rolling" is one of those holdovers that just won't die, even though the Monks who suggested it have retracted the idea long ago. Looks to me like they aren't training anything, just jerking the dog around. Maybe he's trying to teach the dog that humans are irrational crazy creatures because I imagine that's all the dog got out of it. Looks like it might be a malinois, not a GSD, great working breed.

In most cases, yes the lesser wolf submits from subtle cues from the alpha. What I meant to say was that when the alpha wolf is challenged (i.e. for the alpha position) that they will fight/alpha roll the opposing wolf to maintain his dominance.

Corvid, I noticed the biting on the wrist as well. Also, if you listen toward the end, the officer is being told by someone off camera when to roll the dog, and to continue doing it.
Either way, both officer and dog look very frustrated, and the dog unfortunately likely learned nothing from this experience other than to distrust and fear his 'partner'. You shouldn't ever EVER continue training like this when any animal gets that frustrated. You just end up trying to correct more bad behavior formed from the traumatic event. And who knows, all dogs have different personalities. This dog could have possibly gone home that night, had himself some prime rib for dinner, and curled up in his 'partners' lap while having his belly rubbed... Not likely though.