What is the NFHS "Look-Back Rule?"

[hawk65]

So what is the "look-back rule?" 8-7 states when the so-called "look-back rule" goes into effect but it does not define what the "look-back rule" is. Who does it refer to -- the runner, the batter-runner, the pitcher, the shortstop, the coach, the scorekeeper, or who? And where is that explained in the NFHS books? NOT in the definitions and NOT in 8-7. My point is these books don't explain this "look-back rule."