American Football NCAA Rule 5-2-9

No rule decision may be changed after the ball is next legally snapped, legally free-kicked or the second or fourth periods have ended (Rules 3-2-1-a, 3-3-4-e-2 and 11-1). (Exception: The number of a down may be corrected any time within that series of downs or before the ball is legally next put in play after that series.)