This can be a good play when the runner on third is an aggressive baserunner. As the catcher catches the ball, he simply fires the ball to third instead of second. If the runner is trying to get a good jump from third and gets too far from the bag, it's an easy out.
Some coaches have the catcher fake a throw to second and then throw to third. This rarely fools anyone and simply throwing strait to third will give you a better chance of getting the runner.
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