15 The people grieved for Benjamin, because the LORD had made a gap in the tribes of Israel.

Read Judges 21:15 Using Other Translations

And the people repented them for Benjamin, because that the LORD had made a breach in the tribes of Israel.
And the people had compassion on Benjamin because the LORD had made a breach in the tribes of Israel.
The people felt sorry for Benjamin because the LORD had made this gap among the tribes of Israel.