NFHS Rules: Pitcher's Stances.

[bluehair]

In Fed rules when you are in the windup position, you have to disengage before you throw to an occupied base (say 3B). In the set, you do not need to disengage before throwing. If F1 is in this illegal hybrid wind-up postion (the legal set position) and then he throws directly to 3B without disengaging, how can you balk him if he legally made a throw to an occupied base from the set position.

I think this is the reason for the Fed POE. Because Fed has this funky rule difference, if umpires do not enforce it, HS F1 can essentially have the OBR balk rule (the option to throw to a base from this "hybrid" wind-up position).