Is this written down anywhere, or are you just promoting your gut-level sense of a "rule of thumb" from before the onset of the Golden Age of The Police State?
We'll also have to note that Walter Scott was NOT a felon.
And just because Slager assaulted Scott in the back alley doesn't make Scott a felon.
It's more like it makes Slager a vigilante.
You might try googling “fleeing felon rule”.
When you assault a police officer and grab his weapon, you have committed a felony.