I think it is about time Gundy got penalized with this:
Rule 3 Section 5 Substitutions
e. When Team A sends in its substitutes, the officials will not allow the ball to be snapped until Team B has been given an opportunity to substitute. While in the process of substitution or simulated substitution, Team A is prohibited from rushing quickly to the line of scrimmage with the obvious attempt of creating a defensive disadvantage. If the ball is ready for play, the game officials will not permit the ball to be snapped until Team B has placed substitutes in position and replaced players have left the field of play. Team B must react promptly with its substitutes
PENALTY—(First Offense)—Dead-ball foul. Delay of game on Team B for not completing its substitutions promptly, or delay of game on Team A for causing the play clock to expire. Five yards from the succeeding spot [S21]. The referee will then notify the head coach that any further use of this tactic will result in an unsportsmanlike conduct foul.
PENALTY—(Second or more offense)—Dead-ball foul, team unsportsmanlike conduct. An official will sound their whistle immediately. 15 yards from the succeeding spot [S27].
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He has been slow rolling his defensive substitutions for years - ever since they instituted the rule that if the offense substitutes the defense has to be given the chance to. ISU has had to use a TO on more than one occasion because of this tactic. He had D-linemen on Saturday that took almost 15 seconds to make one substitution and the ball was made available for the snap with about 5 seconds on the play clock.
A team shouldn't be in danger of having to burn a timeout or take a penalty when they substitute with more than 20 seconds on the play clock.