Rodney King is a perfect example. The defense for the cops walked the jury through the video: See. Each time they kick his head or pummel his belly, he twitches. A sure sign he is trying to kill them. Naturally, in the face of such persuasive evidence, the jury had to find the poor cops innocent.
The twitching in the final 20 seconds is not what impressed the jury.
What impressed the jury was the fact that Rodney King repeatedly got up and tried to violently assault the cops, over and over and over again.
What happened to those poor cops was a travesty. Yes it was technically wrong that the cops continued to hit him for 20 seconds after he stopped resisting. But considering that they had just been defending themselves from a sustained violent assault, it is understandable that they were not able to instantly turn off the adrenaline.