Baseball's Infield Fly Rule, the Shift, and Other Rules That Confuse Everyone

The Infield Fly Rule activates only when there are runners on first and second base, or bases loaded, with fewer than two outs — and only on a fair fly ball that an infielder can catch with ordinary effort. The umpire must call "Infield Fly" (sometimes adding "batter's out") for the rule to take effect. Its purpose is to prevent an infielder from deliberately dropping a pop-up to create a cheap double play. When called, the batter is automatically out regardless of whether the ball is actually caught, and baserunners may advance at their own risk.

The dropped (or uncaught) third strike rule is one of baseball's most surprising plays for casual viewers. If the catcher does not cleanly catch a third strike, the batter becomes a baserunner and must be thrown out at first base — unless first base is already occupied with fewer than two outs, in which case the batter is simply out. With two outs, the batter may always attempt to run on an uncaught third strike regardless of whether first base is occupied. The play dates to baseball's earliest codified rules and reflects the game's roots in a time when every out had to be actively earned.

For decades, teams shifted freely — stacking three or four infielders on one side of the infield against certain left-handed hitters with predictable pull tendencies. MLB's 2023 rule change ended that practice at the major league level. The regulation requires all infielders to have both feet on the infield dirt and to be divided equally on either side of second base prior to each pitch. Outfielders remain unrestricted in their positioning. The change was one of several pace-of-play and competitive balance reforms introduced that season, alongside the pitch clock and larger bases.

The terms sound almost interchangeable but carry distinct meanings in the rulebook. Interference occurs when an offensive player (batter, baserunner, or even a dugout member) hinders a fielder attempting to make a play. It typically results in the offending player being called out. Obstruction occurs when a fielder — without possession of the ball — impedes a baserunner's progress. Under obstruction, the umpire awards the runner the base they would reasonably have reached. A famous example: if a catcher blocks home plate without the ball, it is obstruction. Fan interference, where a spectator reaches onto the field and touches a live ball, is a separate but related situation the umpire handles with significant discretion.

Many fans believe runners must freeze on the base until a fly ball is fully caught. In reality, the rule is about returning: if a fly ball is caught, a runner must retouch their original base before advancing — this is "tagging up." However, a runner may legally leave the base before the catch; they simply must return to it (or risk being doubled off) if the ball is caught. Critically, under the rules, runners may begin their advance the moment a fielder first touches the ball, not after the catch is secured. This distinction matters most on sacrifice fly attempts at home plate.