If you are your first responder, then you are responsible for a wide array of skill sets. Seeing, recognizing, and believing danger is the first task. Having a plan for avoidance, deselection and escalation is second. If these fail, the fight is on, and it must be won.
From the time that a bad guy chooses you, you will have a very limited amount of time to make a decision. THEY choose how and when. Your actions need to be confident, quick and decisive.