A high school game is scheduled to be seven innings, unlike Major League Baseball, where they play nine. Thus any rule that applies to the “last inning” applies to the 7th inning in high school baseball.
Also high school rules allow for a “ten run rule.” If the home team is ahead by ten or more runs after the top of the fifth inning, or the home team goes ahead by ten or more runs in the fifth or a later inning, the game ends. This is sometimes called the “mercy rule” and helps to ensure that things don’t get out of hand.
[OBR: 9 inning regulation game, 8.5 if home team takes lead in the 9th, or game is otherwise shortened due to a called game.]