once this real cocky cop arrested me and took me to jail. It was really scary. Several years later i saw him at my wife's class reunion. He kept staring at me like he sorta remembered me and was wondering if he should arrest me for something. Problem was when he nailed me I was skinny and had long hair. Now Im fat and bald and wear glasses. It was pretty funny watching him fret over whether I was some gangster of somebody and he couldn't quite recall despite his keen detective memory. That was a fun night
Morally yes... practically no. While I would praise the morality of any citizen willing to put themselves between an armed brute and a defenseless individual, it would be social, if not physical suicide. There is one thing the state does not tolerate, it is a challenge to their authority, no matter how noble, how just, how cleanly executed. As laws become more unjust and power is abused more and more, sadly, this will become ever more true.
Not being there it's hard to find other examples. The only US cop I know (retired) moved to this country, cheated on his wife, beat his daughter up and the got arrested for impersonating a police officer and for dealing narcotics. He had a medal for good service. I know that a sample size of 1 is meaningless, but it doesn't paint a good image.
What do you mean "source"? Aside from the occasional news story where a cop took things too far, when someone is getting arrested, they cops are in the right, when they have to exert a little extra force when taking someone down.