They gleaned, i.e. they cut off the remainders in the pursuit, and spared none; a metaphor from those who gather grapes or corn so clearly and fitly, that they leave no relics for those who come after them.
Related Commentaries of Judges 20:45
Judges 20:45
45 And they turned and fled toward the wilderness unto the rock of Rimmon: and they gleaned of them in the highways five thousand men; and pursued hard after them unto Gidom, and slew two thousand men of them.