It's not a matter of who is better or more justified than the other person. A hurt employee is never a good thing. It is rarely justified. When you employee security guards, the absolutely last thing you want is them being hurt. This isn't the wild west. They are not to put their lives on the line to defend your factory. Sometime that means not doing the justified thing. Sometimes that means backing off and letting the police handle things. If that means retreating if and when a trespasser enters a vehicle, so be it. If that isn't in the manual now, it will be soon.
( I do know that retail security guards are regularly trained not to peruse thieves into parking lots precisely because of dangers created once vehicles are involved. )