[snrmike]

The rule has different stipulations for offense and defense, but it's always a live ball foul.

Since the defense can run players out (or in) at any time before the snap, substitution is rarely called on the D unless a player runs off the field and then back on before the snap.

On offense, the personnel in the offensive huddle often dictates which defensive participants are in or out, so if twelve huddle, illegal substitution (dead-ball foul) is frequently called. If the play starts before the officials notice too many offense participants, the live ball, illegal participation is the call.

Your white hat jumped the gun with the call on the defense in your game.

Here's a quiz: If a player is clearly running off the field and causes no player from the offense to react, what should you call? A substition, or participation foul?