Posterior.
OBR 2.00 · OBR 5.09(a)(5)

Infield fly rule

With runners on first and second (or the bases loaded) and fewer than two outs, a fair fly ball an infielder can catch with ordinary effort is an automatic out — the umpire declares 'infield fly' and the batter is out whether or not the ball is caught. The rule exists so a fielder cannot drop an easy popup on purpose to force a cheap double play.

Key points
  • Conditions: first and second (or loaded), fewer than two outs, fair fly catchable by an infielder with ordinary effort. Line drives and bunts are excluded.
  • The declaration is umpire judgment — made at the top of the ball's arc — and it is not reviewable by replay.
  • The ball is live. Runners may advance at their own risk once the ball is touched, and they are never forced, because the batter is already out.
  • If the ball drops untouched and rolls foul before passing first or third, it is just a foul ball — the declaration is off.
  • A runner standing on his base who is hit by the declared fly is protected; a runner off the base can be called out as well.
In a game

Runners on first and second, one out, lazy popup to the shortstop — who lets it drop and throws to third for the force.

Ruling · Infield fly was declared: the batter is already out, the force is off, and the runners were never required to move. The throw to third means nothing unless a runner left early.

Same situation, but the ball drifts toward the line, lands untouched in fair ground, and spins foul before reaching third base.

Ruling · Foul ball. The infield fly declaration only holds if the ball stays fair; once it is foul, everyone resets.

Why it moves the scoreboard

Erases the defense's double-play incentive on popups: the batter is out automatically, the force disappears, and runners hold their bases unless they choose to gamble.

Related rules