Jersey Not Designed To Be Worn Inside The Shorts ...

[tnolan]

My speculation as to the reasoning behind this rule is this:
to prevent issues with loose shirt tails/strings
logo restrictions
NFHS uniformity (non-individualism)

Here's the issue. #35 is one size and belongs to the school (I'd say in most cases) And if fits A5 2021 differently than it fits A6 in 2022.
Additionally, jersey #12 fits A1 differently than jersey #35 first A5...so uniformity can be difficult.

Normally, I'd say if there are extra logos (size M) or whatever, then it's not meant to be worn untucked....but that doesn't mean that it won't come untucked every time the player puts their hands above their shoulders (ie...every single play)

It's normally the least of my worries, but I've seen officials tell players every dead ball to keep them tucked in. It's a waste of breath. Players are wearing them like that for a reason and once again the NFHS is going to have to adapt or change eventually.