What is an immaculate inning?

An immaculate inning in baseball is a remarkable feat achieved when a pitcher retires three batters on nine pitches, all strikes. This means each batter faced is struck out on three pitches, all of which are strikes. It's an extremely rare occurrence, showcasing exceptional pitching control and dominance. Because it requires such precision and the near-impossible feat of throwing nothing but strikes, immaculate innings are celebrated as a significant achievement in baseball.