I should clarify my answer; the calling of an infield fly makes the batter instantly out assuming the ball lands fair. If the ball lands foul, the call is retroactively cancelled. So if the ball strikes the ground and goes foul before it gets past a base, it's just a foul ball, and the batter goes back to bat, even if the umpire called an infield fly.
(this is why infielders should always catch the ball even if the IFR is called - because the ball could spin out foul, or land foul if it's close to the line.)
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