Charles Ellicott Commentary Judges 20:29

"And Israel set liers-in-wait against Gibeah round about." — Judges 20:29 (ASV)

Set liers in wait. —This exceedingly simple and primitive stratagem had also been successful against Ai (Joshua 8:4) and against Shechem (Judges 9:43). Here, as in Judges 20:22-23, the narrative follows a loose order, the general fact being sometimes stated by anticipation, and the details subsequently filled in.