With runners at first, first & second, or first, second & third and 0 or 1 outs, when a batter pops the ball up to the infield or to the outfield where an infielder can easily make the catch facing the infield, the batter is called out automatically. The reason is so that the fielder cannot "accidentily" drop the ball on purpose and then get a double play. The double play could occur because the runners will not be running. So, even if the fielder drops the ball, the batter is still out. The runners can advance at their own risk after the call/catch is made. If any of this is incorrect, please fix it. Thanks. I don't believe the infield fly rule applies when there is only a runner on first, it's when there are runners on 1st & 2nd, or bases loaded. The batter is never out "automatically", it is a judgement call on the part of the umpire as to whether the fielder could have reasonably made the play. Fred - thanks. That sounds correct to me. ETA: Source