Fighting with the Philistines That is, in a posture and readiness to fight with them, as it is explained 1 Samuel 17:20-21, being drawn up in battle array. In the valley of Elah Not, strictly speaking, in the valley, but hard by it, on the side of the mountain, where they faced the Philistines, and showed themselves resolved to fight, if the latter came down from the other mountain to oppose them.
Related Commentaries of 1 Samuel 17:19
1 Samuel 17:19
19 Now Saul, and they, and all the men of Israel, were in the valley of Elah, fighting with the Philistines.