Make sure your victim is facing you.
The common law elements of self-defense are four; be innocent of instigation, be in reasonable fear of bodily harm, use sufficient force only to deliver oneself from evil, and attempt to withdraw.
Once hit and on the ground you are in an altercation and at trial it will be just like the Trayvon Martin killing.
The Tueller Drill informs us that a holstered gun is inappropriate when the assailant is within seven meters. Your SO must be behind you and dialling 911 and you must be yelling before they get that close. You have screwed the pooch at twenty-one feet.
ETA much later: https://en.wikipedia.org/wiki/Tueller_Drill