along with a gun to back you up. Don't bring lethal force into it until you are completely justified in doing so. If he or she pulls a knife, bang. The kick lets you stay out of reach, if you miss, nothing lost, really. Just jump away. If he pursues you, then he's not beating the other guy, and you are at least justified in drawing if he switches his attention to you. If he actually charges you, well, then, all the holes in his chest/head are on him, as they say.
You might want to watch the video before deciding that you'd have the freedom of mobility to do all this.
I'd be curious as to how it would play out, if you assert you did not need to use lethal force, and by involving yourself by kicking him or attempting to kick him, you escalate the situation to needing to use lethal force.