Ok Adventure-few thoughts-
First-did you put this vidio out as a joke? Lets discuss it-starting with the stance.
It appears that if he was not careful he would hit him self in the jaw with his palm if he was not careful-

Secondly-his left arm is vertical in front of his body which prevents him from protection from a stab to his lung/side of neck area.
his legs seem to be next to each other -which messes up balance.
third-no mention at all of striking at the weapon/hand of the attcker..basic and very important.......
I am not a professional knifer but i have had instruction from some highly qualified people
and this will not cut it-(no pun intended)-

Ill leave more professional comments to the guys here who have delt with knife stances and tactics-dont mean to sound negative but there are better vidios out there .
respectfully, WW