We don't know how long is the hold. He stole the phone and could be playing dumb for hours. Cops have things to do and are pretty impatient when you don't comply. If the cops rushed the situation within 5 min, someone should get fired. If this took 15+ min and isn't getting resolved, it's a different story. Our criminal system is pretty useless. It doesn't teach people a lesson. I'm all for physical punishment for such as caning in times like this. Wiping them a bunch of times and they will think twice before stealing again. Same for the cops who beat up people for no reason if proven guilty. Then they'll feel how abuse of power and beating someone up would feel.
Putting aside (with some difficulty) what I see as the extremeness of your post overall.........
I would ask; isn't the premise of the justice system that first people get a trial before we convict and punish them?
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The use of force by police has 2 basic justifications as I see it, that are interrelated, but not the same.
The first is self-defense or defense of another (a citizen) the same defense any us would use if we were being attacked, or a member of our family was etc.
The second is use of force necessary to do their job, generally to affect an arrest, but perhaps also to exercise a search warrant or to maintain public order. But the justification is predicated on necessity, "I could not have performed by duty w/o using this level of force'.
In this case, the use of force to drop the individual to the floor may well be justified. The use of firm restraint, or even something a bit more in order to cuff someone not being cooperative may also be reasonable. But kicking someone who is both down and restrained is pretty much a no-go.
Any doubt? Listen to the video where another officer can be heard saying 'Stop, stop, stop, that's enough" When your fellow officer is concerned about your conduct, in the midst of the situation, the look is not good.
In reviewing the video I have extracted this still:
This is immediately prior to the last kick, the man is clearly prone with 2 officers on top of him.
I might struggle with the choice to kick the first time; but perhaps there was a benefit of the doubt to be had (but perhaps not), but there were 3 kicks total.
That certainly appears neither professional nor justified. Though the officer is entitled to due process, just like the suspect here.