In college, this play has bailed us out of a lot of bad situations. It was a play I always like to see "called," because it always seemed to catch the opposing team off guard.
With a runner on 1st and 2nd base is when you want to call this play. Calling this play with 1 or 2 outs is even better. Usually with a runner on 2nd-base, the runner on 1st-base takes a bigger lead and at the same time does not fear a throw from the pitcher. Most runners on 1st-base (with a runner on 2nd) believe that the pitcher is only or primarily concerned with the "lead" runner on 2nd base.
The first-baseman or Manager is usually the one who calls this play, by a certain signal or specific word to the pitcher. With the first baseman playing well behind the runner (not holding the runner on), the pitcher goes into his "stretch." Usually, the pitcher would look at the runner on 2nd, then look home, then back to 2nd (for the second time), then home, as he delivers the ball to the plate (hitter).
In this case (practice the timing to make it perfect), when the pitcher goes into his stretch, he looks at the runner on 2nd, then home, then... just as he starts to look again at 2nd, he quickly turns (counter clockwise) and throws the ball to the bag at 1st base. The first baseman starts his break to the bag (behind the runner), the very instant that the pitcher started to turn his head from home, to look at the runner on 2nd base, for the second time.
The ball and the 1st-baseman get to the bag before the runner on 1st can react. (He had a big, comfortable lead because he thought you were only concerned about the runner on 2nd base). The first-baseman catches a well thrown ball from the pitcher, swipe-tags the runner (now frantically diving back to 1st), and the umpire calls him out.
If you call this play with one out and get the runner out, for the second out, your infielders can play at normal depth for the third out. If you call this play with 2 outs and get the runner out for the third out, you have stopped a potential big inning for your opponents. Practice this play to get the timing right. When you pull it off, you will gladly make this play a "regular" in your defensive arsenal.
During practice of this play, it is important that your pitchers throw the ball to the inside part of the bag. DON'T throw to the first baseman. If he is not at the bag when the ball gets there, it is his fault. If the pitcher throws other than to the bag, it's his fault. But with practice and timing, this play is fairly simple to master.