Judges 9:34

9:34 So Abimelech and all his men came up at night and set an ambush outside Shechem – they divided into four units.

Judges 20:36-37

20:36 Then the Benjaminites saw they were defeated.

The Israelites retreated before Benjamin, because they had confidence in the men they had hid in ambush outside Gibeah. 20:37 The men hiding in ambush made a mad dash to Gibeah. They attacked and put the sword to the entire city.