What is the foul?

[FredFan7]

Illegal formation. Flag at the snap. 5 yards from the previous spot.

[Welpe]

If the substitution is done in an attempt to illegaly deceive the defense, you could also have Illegal Participation. This could also be simply a "talk to" if I see that A22 is covered by a defender and I judge no advantage was gained though I'm not sure you'd like that one, John.

[bigjohn]

3.7.5 SITUATION: Substitute (a) A1, or (b) B1, noticing his team has only 10
players on the field, comes onto the field just as the ball is about to be snapped.
RULING: In (a), A1 must be on the field on A’s side of the neutral zone, inside the
9-yard marks, and not violate the shift or motion provisions. Furthermore, the act
of his coming onto the field must not deceive the defensive team. In (b), the substitution
is legal as long as B1 is on the field on B’s side of the neutral zone prior
to the snap. (3-7-6; 7-2-1,6,7; 9-6-4)

[ajmc]

The difference between being impartial and being an advocate is that although both can read the words of a rule, only one considers how best to apply them to equally serve the interest of both competitors, as well as the game itself.

[bigjohn]

2005 - NFHS Football Rules Changes - Football.Refs.Org

Two changes were approved by the committee to help officials better determine the 11 legal offensive players in the game. The first change will require a mark 12 inches in length, 4 inches in width and 9 yards from each sideline to be located on each 10-yard line. The other change will require all offensive players to be, momentarily, between the 9-yard marks after the ready for play and prior to the snap, and adhere to all other pre-snap requirements. The 9-yard markings are not required on fields that are visibly numbered.

"The Football Rules Committee has considered various issues over the past few years to address substitutions and the balance between offense and defense," said Brad Cashman, executive director of the Pennsylvania Interscholastic Athletic Association and chairman of the NFHS Football Rules Committee. "Teams were reportedly returning to previous practices of hiding players near the sideline, as well as attempting to deceive the opponents with various substitution abnormalities.

"The previous rule requiring each offensive player to be within 15 yards of the ball was inconsistently applied, as it contained no easily verifiable fixed reference point for officials to administer."

In addition to the substitution rule mentioned above, several other substitution and illegal participation rules were revised by the committee to clarify omissions and eliminate conflicts within the rules.

[ajmc]

"Bureaucracy": When rules conflict with common sense, to blindly follow the letter of the rule rather than reason the objective. Good officials make lousy bureaucrats.

[Rich]

I can tell you that my crew will not flag this if the kid is properly covered.

We'll talk with the coach after and remind him to get the player inside the marks, but we're simply not going to flag the first one.

Normally this happens during a hurry-up where they get lined up before I can hit the RFP and the defense is ready, the offense is ready and everyone's waiting on the line to set and for the umpire to spot the ball and for me to blow the RFP. Why should they have to wait inside and then shift into their formation?

It's a rule that was written to combat deceptive substitutions and shifts and I would rather work with the intent of the rule rather than the strict letter of it, regardless of how many case plays someone posts.