“ 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].”

At the game, I saw the referee still holding his hand up indicating to wait, but no one was standing over the center. On the replay, you see the umpire moving away from the center, indicating play can begin. Then he suddenly starts running back toward the center as the snap occurs. I think the umpire messed up, not realizing the referee was still signaling to wait.

Normally, there would be a delay of game penalty either on the offense, or if they are purposefully begin slow, the defense.

I do think Utah was being intentionally slow. USC did this same thing to them a couple years ago - see this link: https://www.utehub.com/forums/topic/can-someone-explain-our-delay-of-game-penalty/