This is not some unique baseball thing. The same problem can easily arise in a softball game. If a team is on defense and a coach calls time and puts in two new players in the field, he can have them bat in the spot for the player they are replacing on defense (which is the default way of handling it) -or- the coach can inform the plate umpire that the substitutes are actually going to occupy different spots in the batting order. For instance, the new F4 is going to occupy F1's spot in the batting order and the new F1 is going to occupy F4's spot in the order.

If the coach doesn't specify this, the umpire can assume that the new F1 is taking the old F1's spot in the order and the new F4 is going to take the old F4's spot.

No new or special rule is required. After all, an umpire doesn't really care where the players play defensively, he only cares where they are going to bat in the order.

David Emerling
Memphis, TN

Which is why the batting order determines the substitutions, not the defense positions. Umpires only need to know defense positions for CR eligibility.

IOW, when SubA for Player2 and SubB for Player5 are reported, they are recorded by the BO, not by defense positions. SubA would then bat in the #2spot and SubB would bat in the #5 spot regardless of where they are on defense.

Of course, sometimes we have to ask "which for which?" when told "Jess and Katy for Melissa and Heather".