Illegal Substitution

[rainmaker]

The wording in the book says, "Penalized if discovered before the ball becomes live."

This is one of those situations where a lot of judgment is needed. Lots of refs will let this go unless it gets to be a problem during that game, but it is technically agains the rules. You as the ref need to keep a lot of different things in mind, such as what the generally accepted procedures are in your area, and how other refs in your association or group will handle this. YOu don't want to be the only one who enforces it, and you don't want to be the only one who lets it go. There's not one right answer for every situation, even though the rule is absolute.