‘ And Yahweh smote Benjamin before Israel, and the children of Israel destroyed of Benjamin that day twenty five eleph and one hundred men. All these drew the sword.'
Twenty five out of twenty six Benjaminite units were destroyed. One unit had probably remained to protect Gibeah. The ‘hundred' men were probably specifically a unit of the men of Gibeah (see Judges 20:15).
The mention of the one hundred confirms that we must look at the numbers carefully. It would hardly be true that they were able to count all the dead or that they should come to such an odd number if they did, a round number and yet not a round number (compare the ‘fifty eleph and seventy', a similar odd round number, slain at Bethshemesh for looking into the Ark. The size of Bethshemesh forbids taking eleph as a thousand, as does the odd round number. It probably meant there fifty captains (or family heads) and seventy other men).
But the destruction of twenty five units was easily assessable and the number of men from Gibeah was counted to ensure that they had all been dealt with (a hundred having been sent, the remainder being in the unit left to defend Gibeah).
“All these drew the sword”, that is, were fighting men.