>>>> UPDATE <<<<
The new NFHS football rule changes were announced. Read about them here.
http://nfhs.org/articles/40-second-play-clock-postseason-instant-replay-among-football-changes/
http://nfhs.org/sports-resource-content/football-rules-changes-2019/
http://nfhs.org/media/1020121/2019-football-clock-operators-sheet.pdf