The infield fly is a rule that comes into effect when there are fewer than two outs, and there are runners on first and second base or when the bases are occupied.
If an infielder can catch a fair fly ball with ordinary effort, the umpire declares the batter out even if the ball is dropped or not caught.
This rule prevents the defense from intentionally dropping the ball to initiate a double or triple play. Major League Baseball designed this rule to promote fair play.