[Manny A]

Originally Posted by Centerfield9

Thank you. Is this in the rulebook?

At mlb.com, they define it this way:
"An INFIELD FLY is a fair fly ball (not including a line drive nor an attempted bunt) which can be caught by an infielder with ordinary effort, when first and second, or first, second and third bases are occupied, before two are out. The pitcher, catcher and any outfielder who stations himself in the infield on the play shall be considered infielders for the purpose of this rule.
When it seems apparent that a batted ball will be an Infield Fly, the umpire shall immediately declare “Infield Fly” for the benefit of the runners. If the ball is near the baselines, the umpire shall declare “Infield Fly, if Fair.”
The ball is alive and runners may advance at the risk of the ball being caught, or retouch and advance after the ball is touched, the same as on any fly ball. If the hit becomes a foul ball, it is treated the same as any foul.
If a declared Infield Fly is allowed to fall untouched to the ground, and bounces foul before passing first or third base, it is a foul ball. If a declared Infield Fly falls untouched to the ground outside the baseline, and bounces fair before passing first or third base, it is an Infield Fly."

My interpretation of the MLB rule is that the batted ball is treated like a caught flyball whether the ball is caught or not, so the runners must "retouch" their base before advancing. ASA rules could be different but I cannot find it in the book.

Something you highlighted is key--"the same as on any fly ball."

There's only one thing different concerning an IFF compared to other fly balls, and that's that the batter is out regardless if the ball is caught. Otherwise, it's a fly ball. No need for runners to tag up if the ball is dropped.

Trust me, you're hearing from umpires who have done this for many years. Give up the argument.