The infield fly rule is explained in the
Official Baseball Rules in two places: • Definitions of terms: Infield Fly • Rule 5.09 (Batter is out) The rule applies only when there are fewer than two outs, and there is a
force play at third base (which means there are runners at first and second base, or the
bases are loaded). The rule does not apply on
line drives nor on
bunt attempts. (See
History, below.) When the rule is in effect, if a
fair fly ball is in play, and in the umpire's judgment is catchable by an infielder with ordinary effort, the umpire shall call "infield fly" (or more often, "infield fly, batter's out" or "infield fly if fair" when there is a chance of the ball drifting foul). The batter will be out regardless of whether the ball is actually
caught.
Umpires typically raise the right arm straight up, index finger pointing up and call to signal the rule is in effect. If "infield fly" is called and the fly ball is caught, it is treated exactly as an ordinary caught fly ball; the batter is out, there is no force, and the runners must
tag up. On the other hand, if "infield fly" is called and the ball lands fair without being caught, the batter is still out, there is still no force, but the runners
are not required to tag up. In either case, the ball is
live, and the runners may advance on the play, at their own risk. An infield fly may be declared by any umpire on the field.
"Umpire's judgment" The infield fly rule is a judgment call, as the rule states that "The judgment of the umpire must govern".
"Catchable by an infielder" A fair fly ball that could be caught by an infielder with ordinary effort is covered by the rule, whether or not it is in the infield, and whether or not an infielder catches it, or even attempts to catch it. For example, if an infielder retreats to the outfield in an effort to catch a fly ball, the infield fly rule may be invoked because the ball could have been caught by the infielder. Similarly, infield fly may also be called if an outfielder runs into the infield to catch a fly ball, if it could have been caught by an infielder with ordinary effort. It may be helpful to think of it as the "infielder fly rule". Specifically, the rule states an infield fly call should be determined by "whether the ball could ordinarily have been handled by an infielder, not by some arbitrary limitation such as the grass, or the base lines. The umpire must rule also that a ball is an infield fly, even if handled by an outfielder, if, in the umpire's judgment, the ball could have been as easily handled by an infielder."
"Ordinary effort" The term "ordinary effort" considers all circumstances, including weather, lighting, positioning of the defense, and the abilities of the players involved in the play. A fly ball catchable with ordinary effort in Major League Baseball might not be in a junior high school game, due to the ability of the players involved.
Foul balls If the fly ball is near the foul lines, the umpire is to declare "infield fly, if fair". If the ball is not caught and ends up foul (including if it lands fair and then rolls foul before passing first or third base without being touched by a fielder), the infield fly call is canceled, and the play is treated as an ordinary foul ball. In contrast, if the ball lands foul and then rolls fair before passing first or third base without being touched, the infield fly takes effect and the batter is out.
Statistics Declarations of the infield fly rule are not included in the statistical summary of a baseball game and are not a separate category in player statistics. A fielder who misplays an infield fly is not charged with an error because the batter is out through the infield fly rule. In fact, the fielder who should have caught an infield fly earns a putout. But a fielder who fails to touch an infield fly that then rolls foul may be charged with an error for letting the ball roll foul; the batter is not out, and the misplay prolongs the batter's time at bat. ==History==