HokiePaul wroteThere is no NFHS rule ... that states players are supposed to retrieve a loose ball.
Nor is there any NFHS rule that states that the official must retrieve a loose ball.
HokiePaul wroteI leave directing players to do things to their coach unless it is specifically addressed in the rules/manual/duties. That's why, for example, we say "you can't play with earrings" instead of "take out your earrings". Directing a player to "take out your earrings" is over-stepping your authority, as is (arguably) directing a player to go get the ball.
So, instead of saying, "Go get the ball", we can say, "We can't play without that ball". Hopefully the players will get the idea, and if they don't, we can come back with, "I'm not getting that ball".