This is a pretty standard test question:
Bases loaded--no outs.
Batter hits a pop up that umpires call an infield fly.
Ball drops to ground, uncaught and all runner take off.
Defense throws home, to third and then to 2B and and the bases are all stepped on before the runners arrived.
( Yes, I know, This team has extremely slow runners.)
How many outs do we have??
The answer is one.
Once the IFF rule is called the batter is out and the force is removed.
If the ball is uncaught any and all runners must be tagged for an out.