Im thinking not to many actually watched the video.
Sitting down/falling on his back, was just one option. They went over a couple and why for each.
I can see the falling on the back working in a last ditch, and/or restricted movement area, but I would prefer the "get off the X" and roll out to the side version.
Regardless what you might choose or think, the reasoning is discussed in the last minute of the clip, and brings up probably the most valid point. The gun person usually stands still/in one place and "tries" to deal, and in doing so, severely limits his options, and stands (no pun), a good chance of losing.
This whole thing was more about ways to deal with the Tueller 21' knife rule, which still seems to be lost on some people. A lot of what goes on in the video, shows it is something to reckoned with, and something to prepare for. Keep in mind here too, these boys both know whats coming and are prepared for it. More than likely, in real life, you wont be the one to know, and youre not likely to respond as quickly.
For those who think a knife isnt a viable weapon at a distance, perhaps you should watch the video, and others like it.
Knife fighting is an art few master. Don't have to be in shape to use a revolver.
Ill bet more have been killed over time (and Ill be nice, and say since the revolver has been around) by "untrained" knife people, than even trained revolver users.
Id like to see a video of what they were doing with the gun guy having a revolver (or pocket auto) in his pocket and his hand at his side, in his pocket, sitting, whatever, do the same drill.
As far as the "in shape" thing, keep in mind the boys in that video appear to be in pretty good shape. If youre not, dont you think your odds are going south pretty quick, if the other guy is, gun or not?
I know quite a few people who carry guns. More than not would have trouble just drawing their guns while quickly moving off line. If that fits you, you may want to think about working on getting into "reasonable" shape. Why make it any easier for someone wanting to do you harm?
It amazes me sometimes how gun people, or even people in general, seem to think/treat the knife as a lesser weapon. Guns "can" be an equalizer, but only if youre prepared, and better yet, practiced to use one.