Illegal Participation
 

My crew had a play this past weekend where the defense had 12 players on the field for a down. We caught it after the ball went live then the running play went for five yards. I was unsure where to enforce the penalty from. We ruled a previous spot enforcement and replayed the down. I thought this was correct but then I check the rule book and noticed that some illegal participation fouls are from the basic spot and others from the previous spot.

Does anyone have a good explanation as to why some Illegal Participation fouls are enforced from the basic spot and others are from the previous spot?

Articles 1, 2, 3 and 4a occur while the ball is live. These are enforced from the basic spot, using all-but-one.

Articles 4b-f are fouls simultaneous with the snap. These are enforced from the previous spot.

"At the Snap" is the key phrase. It makes sense now.

Thanks.

It's not illegal to have 12 men on the field prior to the snap. It's illegal substitution if the 12th player doesn't leave the field immediately after being notified he's being replaced. You guys, technically, should have noticed this before the snap but often times we don't or the ball is snapped as you're recounting, which is what usually happens to me.

I tell my crew to flag it for IS if the 12th man is not on his way off just prior to the snap. This saves them 10 yds.