I find that most people aren't so good at running backwards.
First, most people take mincing, baby steps when in reverse.
Second, pesky obstacles and trip hazards rear their ugly heads.
I find that moving in diagonals off the X works much better. This is an area where training can go a long way to help.
So, for me, a Tueller drill with knife would involve drawing and shooting with one hand, while moving off the line (probably on a 45deg advance to his weak side) and using the free hand to deflect.
Note that if deflecting a knife, the goal in deflecting is to actually deflect the knife hand's arm, about 1/3 to 1/2 way up the forearm. Various techniques can be applied at that point. Going for the knife hand will often as not put your own hand in unfriendly contact with the blade.