OnPCHitMe should prevent combat for non-0 fight
Quoting rot in #2703 (closed)
NPC not fighting back doesn't come from 0 Fight, or at least not only. If a NPC with "OnPCHitMe" declared in their local script is attacked the first time, they can react as long as they have enough Alarm, which suggests that they might not be able to react to being attacked because of OnPCHitMe, but still react to the crime of themselves being assaulted.
However, after the first time, if combat is stopped (and their Fight lowered so they don't attack right away again), they won't react anymore. There seems to be something similar to "GetAttacked" for crime, because the lack of reaction (no fighting back when attacked) also spreads to other NPCs with OnPCHitMe (if it's simply declared, without StartCombat manually added) in the same interior cell after a crime spree is over and if these NPCs were far enough not to react to it directly (AI range?). The only thing that changes in their saved properties is "undocumented" for tes3cmd. If a guard apprehends the player and is paid, this behaviour is reset and the NPCs will fight back again.
Most reports about vanilla behaviour are invalid or inconsistent because NPCs won't react the same way after the first time if you keep testing on them with the console.
Currently OpenMW needs the actor's fight rating to be 0 for OnPCHitMe to prevent the actor from engaging in combat when struck, this appears to be incorrect from my own testing.