As Tefal said really, sometimes when you think you've hit them, you have either just slightly tagged them or you've missed completely. Best thing to do, is suck it up and just try again and get into cover if they turn around and shoot you back.
lies best thing to do is to sprint at them get within poking distance, fire your no scope and then press knife, you hit they die you slash an keep running you miss they get a knife in the helmet.
I swear i can't hit a damn thing any more if I'm not running
