In baseball, this term is used to describe the defensive positioning of players when they are preparing to field a ball for a play at second base, or other double play ball. A double play occurs when the defense gets two outs on the same play. This defensive tactic usually involves the shortstop and the second baseman playing closer to second base, as well as closer to the batter. Should the batter hit the ball towards one of these players, he will react quickly and get the ball to second base in time to force an out there-and potentially get the batter out at first as well. This strategy also requires that a pitcher try to force the batter into hitting the ball on the ground towards the left side of the field.
This defensive strategy is very risky because if the ball is hit hard and fast, the defense has less time to react. Defensive all-stars are usually capable of making the play, but many shortstops and second basemen will struggle to catch a hard hit ball when playing in the shallow infield. To minimize the risk, some managers will also bring their outfield defense in closer to prevent a ball from going too far over the infield and into the outfield. This type of defense is rarely used unless there is already a runner on base. If the defense were to play shallow without a player on base, they would be at a disadvantage because of their decreased reaction time should the ball be hit.