The infield fly rule in baseball and softball prevents a player from intentionally dropping or not catching a pop fly in certain situations in order to get two or three outs instead of one. This rule applies only when there is no more than one out, and only with runners on first and second, or all three bases. When a batter hits a pop fly in fair territory on the infield in one of these situations, the home-plate umpire immediately rules it an infield fly, the batter is out, and the runners can go back to their base or try to get to the next one. If this rule did not exist, a fielder could intentionally drop the ball or not catch it, then easily get more than one out by tagging out or forcing out the runners before they could reach the next base.
Why the Rule Exists
In baseball and softball, when a fly ball is caught in the air, any runners must return to their base before trying to advance. If a batted ball is not caught in the air, a runner must get to the next base before being tagged out or forced out, unless there was not a runner on the preceding base. When the preceding base is not occupied, then the runner does not have to advance. These situations are why the infield fly rule is necessary, and why it applies only under certain conditions.
Without the rule, the runners would not know whether to go back to the base or run to the next base until they saw whether the ball was caught. By that time, they probably would not have enough time to get to the base safely. Also, the fielders would be rewarded for dropping the ball or deceiving the runners into thinking it was caught, because they could more easily turn a double play or even a triple play. In the late 1800s, during baseball's early years, fielders began doing this to turn plays, so the rule was created.
Where the Rule Applies
Despite its name, the infield fly rule sometimes applies when the ball is hit past the infield, because there is no predetermined area where the pop fly must be hit for an infield fly to be called, other than in fair territory. If, in the home-plate umpire's judgment, the an infielder could have caught the ball in fair territory — including in the outfield — with normal effort, it can be ruled an infield fly. So, for instance, if a shortstop could easily catch a pop fly in shallow left field, the umpire could call it an infield fly, even if an outfielder eventually catches the ball. Likewise, even if an outfielder runs in and catches a pop fly on the infield, it still can be ruled an infield fly.
Exceptions to the Rule
Not every ball that is hit into the air on the infield falls under the infield fly rule, even if the other criteria are met. A bunt — essentially, when the batter holds the bat out instead of swinging it at the ball — that is popped into the air is not an infield fly. Line drives also do not fall under this rule. In addition, the rule does not apply when the ball is hit into foul territory, unless the ball hits the ground and bounces or rolls into fair territory before passing first base or third base. If the fly ball hits the ground in fair territory and then bounces or rolls foul before passing a base, then it is merely a foul ball, and the batter is not out.
Situations That Don't Apply
There is no need for the infield fly rule when there are two outs, because there is no incentive for the fielder not to catch the ball — that would be the third out, ending the inning. The rule doesn't apply when there is only one runner on base, either, because the batter should be able to run to first base before the fielders could complete a double play after not catching the pop fly. It also does not apply when there are runners on first and third, because there is no runner on second base, so the runner on third is not forced to advance on a batted ball that is not caught in the air.