Charles Ellicott Commentary Judges 20:25

"And Benjamin went forth against them out of Gibeah the second day, and destroyed down to the ground of the children of Israel again eighteen thousand men; all these drew the sword." — Judges 20:25 (ASV)

Destroyed ... eighteen thousand men. —This second defeat seems to have been due, like the first, to overweening confidence and carelessness. Thus in two battles the eleven tribes lost 40,000 men—i.e., 13,300 more than the entire Benjamite army, which was only 26,700. Such a hideous massacre can only be accounted for by the supposition that the Benjamite slings did deadly execution from some vantage point. Similarly at Crecy “1,200 knights and 30,000 footmen—a number equal to the whole English force—lay dead upon the ground” (Green, 1:419).