In order to make it possible for the force of Israel to keep the field, and do to the men of Gibeah what their wickedness deserved, every tenth man (40,000 in all) was appointed to find provisions for the whole army.
Related Commentaries of Judges 20:10
Judges 20:10
10 And we will take ten men of an hundred throughout all the tribes of Israel, and an hundred of a thousand, and a thousand out of ten thousand, to fetch victual for the people, that they may do, when they come to Gibeah of Benjamin, according to all the folly that they have wrought in Israel.