[bob jenkins]

NFHS rules (but I'd be interested in others).

Two subs approach the sub zone. Sub1 enters the sub zone, meets the player to be replaced, and is released onto the court by R2. Sub2 now enters the sub zone, but the coach immediately calls Sub2 back to the bench.

Can the coach do so without penalty? Are the coach's options YUD or require the sub?

(Clearly if the coach calls Sub2 back before Sub2 enters, the zone, it's allowed.)