Saul lost power through three key events, similar to how he gained it (see study note on 1 Samuel 9:1–11:15):
He offered the sacrifices himself instead of waiting for Samuel (1 Samuel 13:1–14);
he made a hasty oath that endangered Jonathan's life (1 Samuel 14:1–46); and
he disobeyed God by not destroying the Amalekites and their possessions (1 Samuel 15:1–35).