new batter not entered in game

Question
There was a new batter at the plate that was not reported to the umpire or the score keeper. my score keeper didn't catch it until the 3rd pitch of the at bat. since it wasn't right after the first pitch of the at bat the batter was allowed to continue to bat. so the other team didn't enter their sub (the batter) until the 3rd pitch of the at bat. if this happens again when should we report that the wrong batter is batting.

Answer
For high school it doesn't really matter.  This is an unreported substitution, not batting out of order. In high school this is just a warning to the coach and the book is corrected regardless of when it is caught.

In ASA if they get a hit and are on base, report it then.  The runners have to return to the base occupied prior to the hit and the un-reported sub is called out.

Tom