When the Philistines attacked the Israelites, the Israelites ran away from the Philistines, and many fell dead on Mount Gilboa.
References for 1 Chronicles 10:1
The Philistines overtook Saul and his sons, and they killed his sons Jonathan, Abinadab, and Malchishua.
The battle was fierce around Saul, and when the archers located him, he trembled in fear.
Saul said to his armor-bearer, "Draw your sword and kill me with it! Otherwise, these uncircumcised men will come and kill me or torture me." But his armor-bearer refused because he was terrified. So Saul took the sword and impaled himself on it.
When the armor-bearer saw that Saul was dead, he also impaled himself on his sword and died with Saul.
So Saul and his three sons died; his whole household died together.
When all the Israelites who were in the valley saw that the army had run away and that Saul and his sons were dead, they abandoned their towns and fled. So the Philistines came to live in them.
The next day when the Philistines came to strip the dead, they found Saul and his sons lying dead on Mount Gilboa.
They stripped him, carried off his head and armor, and sent messengers throughout the land of the Philistines to spread the news to their idols and to the people.
They placed his armor in their god's temple and displayed his skull on a pole in the temple of Dagon.
When all the people of Jabesh-gilead heard all that the Philistines had done to Saul,
all their warriors arose and recovered the corpses of Saul and his sons. They brought them back to Jabesh, buried their bones under the oak in Jabesh, and fasted for seven days.
Saul died because he was unfaithful to the LORD and hadn't followed the LORD's word. He even consulted a medium for guidance.
He didn't consult the LORD, so the LORD killed him and gave the kingdom to David, Jesse's son.