When it's no-huddle, don't kill the play. Everything is happening so quickly. If the 12th man stays, you've got 15 yards, if the 12th man goes off the field (without doing anything to deceive the opponent), it's 5 yards.
Thanks for the great summary.
In one of my games this year, as the LJ, I had mistakedly counted 12 when the defense only had 11 right as the snap was imminent 1st and 10 at the A15 yard line. It was right after a punt return and the offense had the play ready and were lined up before the ready for play, so I got no signal from my BJ. The defense thought they had 12 as well and a deep defensive back attempted to leave at the A30 yard line but didn't make it. So I dropped my flag and the Qb took the snap and threw the ball almost directly at me, where a WR was lined up and the pass landed incomplete out of bounds. I ran in to report the penalty and that I had a live ball illegal substitution. Luckily the back judge had the correct count and we waved it off.
However, afterwards I was told by the white hat, my mentor, and several others that it would have been IP. This continues to bother me as I don't see how the guy running off on defense "participated", when clearly trying to leave, and not reentering during the down. In addition, at the beginning of the season I was told at the state clinic in no uncertain terms that we should NEVER flag a live ball illegal substitution; it is always an IP, with a 15 yard penalty. The only time we have a 5 yard penalty is if we kill the play. I'm essentially a rookie official, but I don't think I will ever see the logic in this state's position.
Mike in Connecticut