This topic has probably been beaten about quite a bit here. However, I actually had it happen in one of my games earlier this year. A is ahead by 1 pt. with under 2 minutes remaining. B is out of timeouts and A has a 2/8 from the A-12. A sweeps left and is stopped at the line by B55. Immediately, and legitimately at the end of the play, B78 falls to the ground with a muscle cramp. During the injury timeout, my Umpire, who also officiates at the college level states that if we go with a 25 play clock, B's own injury is advantageous to them, gaining them 15 seconds, and that we should be going with a 40 second clock. We decide to go with the 40 and A got a first down on the next play anyhow. Justified?
1.6 The referee has authority to rule promptly, and in the spirit of
good sportsmanship, on any situation not specifically covered in the rules.
The referee’s decisions are final in all matters pertaining to the game.
I've gotten some differing opinions when I ask around. This really should be a NFHS rule change to a defensive injury or helmet off goes to a 40 second clock.