The only difference between an infield fly and any other fly is that the batter is out when it is declared, and the ball does not have to be caught. Because the batter is declared out the runners are no longer forced to run, but they may run if they wish, at the risk of being put out. If the ball is caught they must tag-up before running, the same as on any fly ball. If the ball is not caught they may run without tagging up, the same as on any fly ball.

If the umpires forget to call an obvious infield fly, the rule is assumed to have been called and the batter may still be out. If the umpires forget to call it, the defense is not allowed to get 2 or more outs. They can only have one. If the ball is dropped and nobody is put out, the batter is called out. If the ball is dropped and 2 or more runners are put out; the batter is out and the other runners are returned to their original bases. This is Official Baseball Rules. If a fly ball first lands untouched on foul ground before first or third base and bounces untouched into fair territory, it is an infield fly because it is now a fair ball and the batter is out. If the fly ball first lands untouched in fair territory before first or third and bounces untouched into foul territory, it is just a foul ball.

The Infield Fly is a judgment by the umpire that the ball could be caught with ORDINARY EFFORT by a player who was stationed in the infield at the time of the pitch. It is not automatic just because it's a pop-up in the infield. Ordinary effort is a judgment, but it usually means that the fielder did not have to sprint for the ball or make a catch on a fast run. It means he is underneath the ball and relatively motionless. The ball could be caught in the outfield and still be an infield-fly; if the fielder got under it and was relatively still. An outfielder could catch the ball and it is still an infield-fly; if an infielder could just as easily have caught the ball.