The verb cut down
translates the Hebrew verb that appears also in Judges 19:25, there translated abused.
The significance of this becomes obvious: according to God’s justice, the Benjamites suffer an appropriate punishment for allowing such an awful crime in their own tribe.
45 And they turned and fled toward the wilderness to the rock of Rimmon. Five thousand men of them were cut down in the highways. And they were pursued hard to Gidom, and 2,000 men of them were struck down.