Unlike pro rules, NFHS rules have no "per inning" limit. A team gets 3 charged defensive conferences per game. On the fourth conference, the coach must change pitchers. So the coach can come out three times in the same inning and not change pitchers. On the fourth trip, whether in that inning or a later inning, he must change pitchers. Also, under NFHS rules, conferences are cumulative and do not "reset" when a new pitcher enters the game. Example: A coach makes has 2 charged conferences with his starter during the first inning. During the third inning, he comes out again and changes pitchers. That visit is not a charged conference because he made a pitching change. If the coach comes out again later in the game to have a conference with his relief pitcher, that is the team's third charged conference of the game even though it is with a new pitcher. The next time he comes out (and every time after that) he has to change pitchers. Once you reach four charged conferences, each conference will result in the coach having to bring in a new pitcher. The purpose of the rule is to speed up the game and avoid repeated mound visits.