I found the game on NFHS Network so I will pull the clip later today and we might can see what the aftermath was.
I am curious as what happened on the previous down. I think we've all been assuming that Team A only had 11 players on the field during the down in question. That is probably a relatively safe assumption. But, after the previous down, another A player must have left the field, to make a player vacancy for the substitute that did run onto the field. (Unless Team A played with only 10 players on the previous down??? I suppose it could have happened.)
If this was a crew of 7, and a Team A player left the field after the previous down, the deep wing on that side should have observed that, which should have raised a red flag for him, i.e., he should expect to see a substitute come off the sideline. Well, a sub did come off the sideline. So, all is good, except that the guy holding his wrist is 'apparently' leaving the field. Again, this should have raised a red flag for the deep sideline guy, in terms of expecting to see another substitute come off the sideline to replace this guy that appears to be leaving the field. When he doesn't see a sub, but sees the player stop near the sideline, he should now be on high alert for a 'hideout' play.
Apparently, the specific rule covering this action is unclear in NFHS, as well as whether it is a live-ball foul or a dead-ball foul. But, it appears that everyone agrees that it is illegal, and that is the most important thing. Regardless of which rule set under which the game is being played, this is an egregious act of illegal deception. Call it unsportsmanlike conduct, call it illegal participation - but do not allow the score, and hang 15 on 'em at the previous spot (if live-ball), or succeeding spot (if dead-ball). As I have said before, this is cheating - plain and simple.
Note: There is deception in football. Like, faking a hand off; almost everybody on the team running in one direction while the BC runs in the other direction; faking a kick and running/passing/handing the ball; signaling for a fair catch and faking like you are catching the ball and letting it bounce into the end zone. But, hideouts, fumblerooskis, concealing the ball in your clothing, bounce-backward pass-pretend-it-was-incomplete-forward-pass plays, etc., are simply illegal deception.
Let's have the courage to make these calls.