The Illinois High School Association -- known as the IHSA -- oversees all high school sports in the state. The IHSA uses the same rules that the National Federation of High Schools uses to ensure each game is played fairly and that both teams can compete while following the same rulebook.
Many high school sports leagues in Illinois conduct postseason tournaments to determine champions. Seeding in those tournaments is based on regular-season standings. However, if your team is tied in the standings at the end of the year, the following tiebreakers are used to determine higher seeding in the following order: head-to-head wins; fewest runs allowed in league games; most runs scored in league games.
There is no pitch count in IHSA baseball. However, once a manager takes his pitcher off the mound, the pitcher cannot return to the mound even if he has not left the game. For example, the manager may replace his pitcher by having the pitcher play in the left field spot and having the left fielder pitch. The manager cannot have those players exchange positions again at any point in the game.
The designated hitter is used in Illinois High School baseball: A hitter may bat for the pitcher. The manager is not compelled to use a designated hitter if he wants the pitcher to bat. If the manager chooses not to use the DH at the start of the game, though, he can't change his mind and use a DH later in the game.
The IHSA uses the "mercy" or "slaughter" rule to end one-sided baseball games. If your team is ahead by 15 or more runs after four innings, the game is concluded after the trailing team takes its at-bat in the fourth inning. If your team is ahead by 10 runs or more after five innings, the game is concluded.