Contradiction with 2 Samuel 1:6-10
2 Samuel 1:6-10 suggests that an Amalekite killed Saul, whereas 1 Samuel 31:11 describes his death in battle by his own hand, witnessed by his armour-bearer.
2 Samuel 1:6-10: And the young man that told him said, As I happened by chance upon mount Gilboa, behold, Saul leaned upon his spear; and, lo, the chariots and horsemen followed hard after him.