Earlier, the men of Israel and the men in the main ambush had planned that when Gibeah went up in smoke, the fleeing Israelite troops would know that the ambush had succeeded. So the great cloud of smoke was the agreed-upon signal for the Israelites to turn and counterattack their pursuers (Judges 20:39). It would be the assurance of victory.
38 Now the appointed signal between the men of Israel and the men in the main ambush was that when they made a great cloud of smoke rise up out of the city