Garthanos
Arcadian Knight
As far as I'm aware, that's not a rule.
As I said, it's an intelligent tactic to focus attacks on a current threat
Its a normal tactic for animals too.... And you wouldnt believe how well water buffalo fight as a team or how the whole herd will run back to protect a child who was singled out by a pack of lions... or how effective they can be against them.
Humans becoming over focused because they fight out of rage... instead of need might result in ravaging a downed foe more even than other animals.... and even then we are not likely to do it efficiently but rather wildly ... not a coup de grace like (ask the cops)
Dispassionate assassin like behavior is not that easy for anyone but sociopath folk.
Adrenaline rushes make wild hacking slashes easy precision cut its throat behavior is tough.
Hell the monsters might not even recognize that the hero attacking now is the same one it took down a few moments ago... or it might just be confused and frightened by the fact that you sprang back to life.... human tenacity and endurance can be freakish (studies comparing our ability to handle activity in high heat ... with that of various animals including many of those we think are physically superior are very surprising)
If you want the monsters to be so distracted by the blood they stop to eat or so in to the fighting that they dont stop when the hero goes down... that is your choice.. but it might just be a human behavior not an animal one.;-)
Dragging away what they think are a dead foe would be very realistic.. hey thats food I just killed Im keeping it..
Cheers