Adam Clarke on 1 Samuel 18:7

Saul hath slain his thousands - As it cannot literally be true that Saul had slain thousands, and David ten thousands; it would be well to translate the passage thus: Saul hath smitten or fought against thousands; David against tens of thousands. "Though Saul has been victorious in all his battles; yet he has not had such great odds against him as David has had; Saul, indeed, has been opposed by thousands; David, by ten thousands." We may here remark that the Philistines had drawn out their whole forces at this time: and when Goliath was slain, they were totally discomfited by the Israelites, led on chiefly by David.