What is the Infield Fly Rule?
  
  The infield fly rule is one of the most misunderstood rules in
  the game of baseball. Little league coaches struggle to
  understand it, and the rule has even mystified professional
  managers at times. To begin, the infield fly rule can only come
  into effect if: 1) there is less than two outs in the inning; 2)
  there are baserunners on first and second base or first, second,
  and third base; and 3) the batter must hit a fly ball in the
  infield area. If these three elements are present, the umpire
  should call "infield fly rule - The batter is out." At that
  point, even if an infielder dropped the ball, the batter is still
  out.
  
  The infield fly rule originated to protect baserunners from
  crafty infielders. For instance, before the rule came into being,
  if baserunners were on first and second and a fly ball was hit in
  the infield to the third basemen, the third baseman might let the
  ball fall in front of him on purpose. He could then pick up the
  ball, tag third base to force out the runner on second base and
  then throw to second base to force out the runner on first.
  Accordingly, by being crafty, the third baseman was able to
  secure two outs for his team rather than just one if he caught
  the ball.
  
  The infield fly rule is a judgment call for the umpire. If the
  umpire deems a fly ball catchable in the infield with the
  appropriate baserunners on base and less than two outs, then the
  batter is out. Even if an infielder drops the ball, the batter is
  still out. However, if the umpire calls the infield fly rule and
  the ball drifts into foul territory and the third baseman, for
  example, drops the ball, the batter is no longer out. It is
  simply a foul ball at that point and the batter can again step up
  to home plate. In such a situation, the proper call by the umpire
  should be, "infield fly rule, if fair."
  
  Baserunners are often confused when an infielder drops the ball
  after the umpire calls the infield fly rule into play. In short,
  baserunners are under no obligation to advance and they cannot be
  forced out. If the infielder drops the ball, the baserunners can
  advance at their own risk. Should they choose to advance, they
  need not tag up because the ball was not caught. If the ball is
  caught in the infield area after the rule has been called into
  effect, the baserunners can attempt to advance should they so
  desire, but they must first tag up, as with any other regulation
  fly ball.
  
  
  
  
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