שופטים, פרק ט׳, פסוק ל״ד

Acting on the advice he received, Abimelech launches a covert military strike against the city of Shechem under the cover of darkness [מלבי״ם, ביאור שטיינזלץ]. To maximize the effectiveness of the attack, the primary approach among commentators is that the army is divided into four separate units to set up an ambush. The strategy behind splitting the forces is highly tactical [מלבי״ם]. Two of the units are positioned directly at the city gates to block any movement in or out, while the other two units are tasked with attacking anyone caught out in the open fields.

This carefully planned ambush serves as the opening move of a much larger military campaign. When Gaal eventually marches out to engage Abimelech in battle, he is met with a crushing defeat. As his forces retreat toward the city gates, they suffer heavy casualties along the way. The military disaster creates a perfect opportunity for Zebul, who has remained inside Shechem. As Gaal and his surviving men fall back, Zebul locks the city gates, trapping them outside. He then persuades the residents of the city to permanently expel Gaal and his brothers, arguing that Gaal is entirely to blame for the devastating loss they just endured [אברבנאל].