So the children of Benjamin saw that they were struck; for the men of Israel gave place to Benjamin, because they trusted to the liers-in-wait whom they had set against Gibeah.
"They enclosed the Benjamites round about"  (Judges 20:43).  The slaughter of the inhabitants of Gibeah and the burning of the city provided the pre-arranged smoke-signal for the Israelites to turn and engage the Benjamites.  At the same time, the liers-in-wait were free to press the attack from the direction of Gibeah, thus "surrounding" the whole army of the Benjamites and fighting them on all sides  (Judges 20:43).