[JRutledge]

I cannot speak for what you have seen, but I have called this several times on the defense as a Back Judge as I am the primary on defensive substitutions.

I am sorry I do not have my rulebook, but I have my casebook. Actually based on what you have said it should have been illegal participation, not illegal substitution according to 9.6 Comment (which references 9-6-4a). Now it is possible that the official also judged more than 11 on the field at one time and the play went off. You can have a live ball substitution foul, but this does not sound like this is what it was. Then again as a coach you have never heard of the foul, so it is hard to know what really happened.

Peace