Charles Ellicott Commentary 2 Samuel 21:15

"And the Philistines had war again with Israel; and David went down, and his servants with him, and fought against the Philistines. And David waxed faint;" — 2 Samuel 21:15 (ASV)

Had yet war again. — This, like the preceding narrative, contains no note of time except that it occurred after some other wars with the Philistines; but this is only to say that it was after David ascended the throne. From the latter part of 2 Samuel 21:17, it is clear that it must have been after David had become king of all Israel, and probably after he had become somewhat advanced in years. In 1 Chronicles 20:4–8, much the same paragraph is placed immediately after the war with Ammon; but this seems to be a mere juxtaposition rather than designed as a chronological sequence.