This is 80 % of my practice for the past 25 years. In a nutshell, QI means that to be sued personally, in his individual capacity, an officer must be shown to have violated the Constitution and that the right he violated was "clearly established" at the time. The theory is that we need officers to make decisions rapidly and there is usually not time to reflect and think everything through. They should not be personally held liable unless it is clear and obvious that what they are doing is unconstitutional.
Typically, that can be done in two ways: find a prior case decided on materially similar circumstances from either the US Supreme Court, the federal court of appeals in your jurisdiction, or your state supreme court, which decided that the same action was unconstitutional; or, show that it is so obviously wrong that no reasonable officer could believe it to be lawful.
The theory is that under either standard you are giving breathing room to the officer to use judgment and not fear getting sued if he turns out later to be wrong. He should be given fair notice of what the parameters are.
So take the Atlanta case. Now, that is within my federal experience because it is within the 11th Circuit Court of Appeals, which is comprised of Florida, Georgia, and Alabama. The question is, where you are in process of arrest and the suspect punches you, fights with you, grabs your taser and runs, but then fires it at you as he runs, is it clearly unconstitutional to use deadly force?
The answer is a resounding NO. This is not simply shooting a non-violent immediate risk felon in the back as he runs, which is unconstitutional. This is shooting one who is running away but in that process is firing the taser at you. There will be no case on point on the issue, and so the issue will devolve to whether any reasonable officer could believe that to be lawful, and the answer to that question is clearly yes.
Bear in mind this has nothing to do with the criminal case. I think that is weak for a ton of reasons, but that's not my usual area. I'd be stunned if in the inevitable civil suit the officer did not get qualified immunity.