How high is a fly?

[Dakota]

Once the fly ball has enough of an arch to raise the question in your mind, the deciding factor is this "ordinary effort" thing, IMO.

ASA (I know this is a FED question, but it does add to understanding, IMO) says a line drive must be hit sharply and directly into the field.

If the ball is not hit sharply and directly, has enough of an arch to raise the question, and the fielder has enough time to line up the catch and then decide to step back a couple of steps and catch it on the bounce, it sounds to me like an IF. But, of course, HTBT.