My instructor told me this in so many words, but even when it comes to friends getting their ass kicked...it's not my life in danger. The attacker is whipping their ass, not mine, so I could walk away. Therefore, pulling my weapon to assist is against the laws...that was told to me.
The cardinal rule is you engage to 'stop a threat against you'....no one else...other than family of course. To tell a dispatcher they are in fear of their lives cause they see a man beating a chic within his own car....c'mon!