There appear to be multiple interpretations of this, with shades of grey in the middle.1. Rule 1 of the main rules applies to security.
The only exception is that security is generally considered to be armed with non-lethal methods to control a situation. Therefore, where reasonably possible, security is expected to use non-lethal methods first in a conflict before escalating to lethal methods.
Notably some of us have taken this as implying that security should be exclusively using non lethal force (that is stun weapons and disablers, non harmful if you prefer for clarity) unless circumstances justify (armed, suitably hostile, can not be locked down due to hulk, lacking an arm, etc etc).
There appears to be another take where this means as long as you stop short of actually killing the other person then that's okay (as far as I understand the take).
There's probably other takes too.
Given this ambiguity, and the grey scale within (is beating them to crit okay? -50 health? breaking their limbs? - this is literally part of terry's history) where is the line exactly?
My take is that security should generally not be harming their targets in any way (doing so being assault and in its self a crime!), unless the target is an antagonist or acting like one (noting that non antags attacking security harmfully are breaking the rules and would be bwoinked for that, also permitting security to do whatever to the attacker for acting like an antagonist in most cases).
I guess some further guidance to get us all unambiguously on the same page might be in order here?