that sounds needlessly crippling and terrible for the same reason taboo's drop-weapon-if-you-get-shot-really-hard script is terrible
if you have this script running on a server, this would mean two things. one, any weapon that would kill in two hits functionally kills in one because doing more then half damage in a single shot would render the other player instantly helpless and unable to protect themselves. THAT means that their aggressor has a free shot, and that means the affected player is forgeted beyond belief
second it's not even like a curt like 'oh, i've been outmatched, forget' death. it's one of those stuffty boss battles deaths where you know you're dead because regardless of whether or not you survived the initial shot you're going to die because of stuff you literally cannot respond to anyway, and thus the entire span of time between 'getting killed' and 'actually dying' is a sudden frustrating swerve
why would you ever need this in the first place
Way to stuff on someone's idea.
A good reason for needing this is being a better substitute for 1 hit kill weapons-- at least you still have a small chance of doing something rather than just dying instantly. This doesn't have to be applied to just strong weapons, as this was just an idea. It doesn't have to make you completely useless but can still be some sort of a debuff. I don't think this is a bad idea but certainly should be revised a different way.