The J-Hook.
To aid in the explanation of the “J Hook” that I was talking about here, I cranked out this quick illustration. The red guy is the attacker, the blue guy is the defender. The darker colored ones are the initial starting positions and the light colored ones are the finishing positions.
From the illustration you can see that the defender is backing up on a path parallel to the path that the bad guy is charging down. While the defender is backing up, he is doing so across terrain that he has already seen. We have been doing this with Simunitions for years, and when executed correctly it works at much shorter distances than 21 feet, and the defender can easily get multiple shots on the attacker.
There have been some questions about Rule 4 issues. In the real world there aren’t very many “Safe” backstops. There are some that are safer than others. Rule 4 doesn’t require a safe backstop, it requires that you be aware of your target and aware of what is behind and beyond your target. It is up to the individual to decide if they are willing to accept responsibility for where the bullets end up.
As Jeff Mau stated:
Rule number 4 is simply to know your target, what is beyond it and being willing to accept the consequences of what you shoot. It most certainly does not mean you can only point your gun at a berm or something else that will stop a bullet. If given the distance, I will likely not immediately shoot the crazy guy making threats with a knife standing in front of a school bus with little kids inside. If possible, I will maneuver to avoid the possibility of hitting an innocent. However, if that same crazy guy has a bomb strapped to his chest, then I have no issue taking the shot and possibly jeopardizing the kids.