In one sentence, describe what the following article is about:

It is designed to get your heart rate up and maybe some adrenaline going which will give you a mild tunnel vision effect. Before you do a drill, with your firearm securely holstered, do 20 or more push ups. Go until you have a bit of a burn and you are getting out of breath. Jump up and do your drill as soon after as possible.  You will find that acute aiming is much more difficult, though general flash sight aiming shouldn't be too much different; this is why it is so important. This becomes a problem if your pistol is resting against something or the front of the gun is pressed into something soft. A simple drill to keep the bad guy off of your gun in a close quarter situation is to put your support arm straight in front of your chest bent at a 90-degree angle. This keeps the bad guy off you, while your firing arm is lowered near your hip. For practice: a tall target you can lean up against your arm and fire into it is good (make sure the target is soft, so the bullets don't ricochet and it doesn't splinter — make sure you shoot straight forward so you don't hit your arm). A couple times is all you need with this drill, just to give you the feel. Have a center-chest-sized target (10+ inches) setup 15–20 yards (13.7–18.3 m) away. Start your sprint at it, when you feel you are close enough to hit the target while moving, slow down to a crouched walk with your knees slightly bent (to keep your upper body smooth) and shoot the target.   Add different things while running: have a friend tell you when to start shooting (at random times). Or start running at the same time a friend starts reloading. Have the friend yell when he is done to let you know to start shooting. It can become a reloading vs. sprinting contest (it will also give you an idea of how long a reload feels like if you need to rush someone). If your location allows, stand 15–20 yards (13.7–18.3 m) away from your target. Have another person stand well off to the side pointing at a different target. The person standing to the side will have one round in the chamber and an empty magazine, with a loaded magazine in easy access (i.e. magazine pouch). You should have your gun out at and the ready. The other person will fire; you start running at your target. When you are close enough to get good hits, you shoot; if the other person is able to reload and fire at his target before you shoot, he wins. It is best (for safety reasons) for the other person to be aimed and shooting at a target which is different direction than yours, so at no time will one person be in front of someone else's muzzle. Additionally, you can try reloading while running at the target, then shoot the target when you are done (this is the most advanced version of this drill).

Summary:
This drill can be added prior to any other drill. Most semi-automatic pistols will not fire if the slide on the gun is not in battery (full-forward) position. Charging a bad guy seems like a stupid idea in most cases, but if the bad guy is reloading, or otherwise distracted, it can be of great benefit (you may be able to catch them by surprise or disarm them).