NFHS rules do not require the tackle to be covered. The only requirement is that you have "at least" 5 players on the Line of scrimmage and no more than 4 in the backfield. Obviously that's not the full 11 players and you would typically have 7 players on the line of scrimmage including 2 ends (either tight or split). Many teams will run an unbalanced line that leaves the tackle or even a guard as the last player on one end of the line which is perfectly legal - except... The INFC, however, has a rule that say a 2-stripe player cannot be on the end of a line and must be covered up by another player.