I would like to get a feel for how close everyone is calling illegal substitution for not leaving huddle immediately. I was a spectator at a HS game last Saturday and that foul was called three time. I wouldn't have called any. How do you define immediately? I try to use discression - advantage, disadvantage - the spirit of the rule.
Comments?

I think just a couple of seconds is all the time that should be given. The advantage that is gained, is the more time given with 12 or more players on the field is all the less time for the opponent to make adjustments.

When you say it was called three times the other night, how long do you think they were being given?

It was called like the NCAA, when the huddle broke and one player went to the sidline. In my game this past Friday, the offense played 4 plays with only 10 players. If I had called a foul when I saw a player from the huddle leaving the field, I would have been wrong since he was the 11th player.

A good rule of thumb is to allow 3-5 seconds for the substitute to alert the replaced player. The book states "immediately" as the time frame but most interpret that as within 3-5 seconds.

Now, I would give B a little more leeway than A because B really doesn't gain a huge advantage by having 12 on the field. A already has chosen its play and are in the huddle while B is getting it sorted out. I wouldn't give B too much more time than 5 seconds, but I think A certain has he bigger advantage when it comes to having too many men on the field. Plus, if it doesn’t get called before the snap they get nailed with a 15 yard penalty.

I would have called all three, as you describe. I might give a little more leeway for a player who left before breaking the huddle... but if a kid came into the huddle, making 12, and the 12th waited until the huddle broke to leave, there is a very real chance of deception (intended or not), and this is what the rule was intended to prevent.

You don't toss the flag until after the count as been made and in fact determined to be 11. Hopefully, this is being done before the huddle is over. Only then, can that replaced played heading to the sideline, be the twelve man.

I also hear 3 to 5 seconds as the accepted norm. 5 seconds seems just too long to me.

I think you also should consider 'how' the 12th player left the field. If a late arriving sub enters the huddle and the huddle breaks immeadiately upon his arrival. The player now leaving the field does so in a manner that does not leave any doubt to his intentions. I don't see this as a penalty under any circumstance. However, if the replaced player now slowly moves toward the sideline and there is doubt whether he's assuming a position in the formation or just slow gettting off I'd flag him.

I agree. In the NF "breaking the huddle whith 12" is not a foul. A replaced player not leaving in a timely manner is.