We’ve had a blindside blocking foul in NFHS for a couple of years. It’s not hard to distinguish an illegal blindside block from a legal “unseen” block, although it does require officials to be vigilant, especially on kick and COP returns, and reverses. The criteria for the foul includes “forceful contact”, and we also have an exception for extended hands.
I’d say my crew has averaged 3 BSB fouls per year over the past two seasons.