The front hand gives distraction, so you block it, but the back hand facilitates extension and ease of deadly attack.
So you block the front hand throwing it down on his knife hand, slip a counter strike anywhere ribs or face if you can (whatever is more efficient) and move to control his arm and neck.
You defend according to the attacker's positioning. Principles are applied throughout everything. If he moves backward then you can’t catch him. Instead you immediately kick to the pelvis area, either the groin or tail bone according to the angle he presents himself.
If he moves in, you pull his arm to take him off balance and foil his stab, following with a knee kick to his tailbone.
You need to cover all the options even if they are created in the classroom by all types of personalities of students. What is the sense in teaching advanced scenarios to those not yet adequately skilled in foundational principles?
While other instructors may revert to shadow boxing, we revert to forward attack in the long range, always closing the gap. In the short range we seek control and balance shake until the deadly or forceful devastating blow is applied.
You need to go over the whole picture so students can rehearse the prior training steps if they cannot prevail successfully. So you give them a complete training system and show them how to find the errors and how to correct it.
The first time people see it they might be overwhelmed a little, not sure what is expected from them and how to apply it.
But after 72 hour is settles better in their brain and bodies, from empirical experience. In fact going over all the aspects of training also motivates the students and gives them the a path to see where they are coming from and where they are going to.