John Gill Commentary 1 Samuel 31:1

"Now the Philistines fought against Israel: and the men of Israel fled from before the Philistines, and fell down slain in mount Gilboa." — 1 Samuel 31:1 (ASV)

Now the Philistines fought against Israel
Being come to Jezreel where Israel pitched, (1 Samuel 29:1 1 Samuel 29:11); they fell upon them, began the battle:

and the men of Israel fled from before the Philistines;
at the first onset, as it should seem:

and fell down slain in Mount Gilboa;
which was near, and whither fleeing they were pursued and slain, at least great numbers of them.