[just another ref]

Originally Posted by M&M Guy

That's exactly where we disagree. 4-23-2 deals with establishing legal guarding position. 4-23-4(b) and 4-23-5(d) deal with how airborne players are treated differently. If defending an airborne player is no different than defending any other player, in regards to LGP, then why do the rules list an airborne player separately and change the wording to "legal position"? Again, you (and others) are adding the word "guarding" to those 2 rule sections where it doesn't exist. All those sections mention is "legal position", and we know there is a difference between those two terms. And, because of that, it doesn't allow for the same movement allowed by the LGP rules in 4-23-3.

I understand it doesn't "seem right" that a defender would not be allowed to move away from an airborne player, and it's probably not how it's called in practice. But that's not how the rule is written.

It is possible to have a legal position and not have legal guarding position. It is not possible to have legal guarding position without have a legal position. In the OP the defender has both. But even if he doesn't, if he is standing with his back to A1, it is not possible for him to commit a foul by retreating after A1 becomes airborne.