Nothing kills a baseball rally faster than a double play, so much so that it has been affectionately named "a pitcher's best friend." There are many ways defenses can turn a double play, but here are the most common plays in which teams turn two.
The 6-4-3
"6-4-3" is shorthand for the most common double play in baseball. With a runner on first, a ball is hit to the shortstop (the 6 position if you're marking up your own scorecard) who flips the ball to the second baseman (4) to force the runner out at second. The ball is then thrown to the first baseman (3) to force out the hitter.
Strike Him Out, Throw Him Out
Of all double plays, this one can be the most deflating for an offense. The double play begins when a runner on base attempts to steal either second or third when there are two strikes on the batter. If the batter swings and misses, and the base runner is thrown out on the steal attempt, you have a "strike him out, throw him out."
"Freeze on a Line Drive!"
One of the first things little leaguers learn is to freeze on a line drive. That is, if you're a base runner and a ball is hit hard on a line drive, you shouldn't run until the ball clears the infield and lands on the ground. But, even major league players forget this rule; if a line drive is caught and a runner doesn't get back to the bag in time, he's forced out for a double play (often called "doubled up").
The Outfield Assist
If a game is tight and in the late innings, a play at the plate can be the difference between a win and a loss. If there are less than two outs and a runner on third, a hitter will often try to hit a fly ball deep into the outfield so the runner on third can tag up and score. If the outfielder can make the catch and throw the runner out at the plate, a double play saves a run.
There are many other exciting ways a defense can turn a double play during the course of a baseball game, but most baseball fans see the four plays above the most. But as the old saying in baseball goes, you see something new every game. Don't blink or you might miss a new double play.

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