The battle lines are drawn as a fierce civil war erupts among the Israelites. The warriors of the tribe of Benjamin launch a desperate and aggressive charge from their city, clashing with the attacking forces of Judah. The result of this initial conflict is a devastating defeat for the attackers. Tens of thousands of Israelite fighters are struck down, leaving a massive number of casualties scattered across the battlefield [מצודת דוד, ביאור שטיינזלץ].
Such a crushing defeat for the united tribes of Israel raises a difficult question, as they had embarked on a just and moral campaign. The primary approach among commentators is that this devastating loss was not the result of military superiority or tactical failures. Instead, it was a direct punishment from God for a previous sin, specifically the Israelites' collective silence in the face of the idolatry known as Micah's idol.
The Israelites displayed immense zeal and moral outrage over the horrific injustice committed against the concubine at Gibeah, quickly mobilizing for war. However, they failed to show that same determination for God's honor when an idol was openly set up in their midst. The heavy casualties they suffered served as a sharp divine rebuke. They had ignored the honor of God by refusing to protest or fight to eradicate idolatry, yet they rushed to wage war for the honor of flesh and blood [רש"י, רד"ק, מצודת דוד].