NFHS - Same numbers

[ajmc]

Originally Posted by BktBallRef

Are they participating during the same down if one leaves the field and another enters the field before the down begins?

Considering the NFHS Rules definition of "Participation"
(NF: 2-30) "Participation is any act or action by a player or non-player that has an influence on play." it appears the prohibition would only apply to a substitution performed when the ball was alive.