The flight and capture of a defeated leader ends in a harsh and unusual act of physical mutilation. The ruler is known as Adoni-bezek, meaning the Lord of Bezek, a title structured similarly to Adoni-zedek [רד״ק]. Despite having been a powerful emperor who previously subdued seventy kings, his territory in Canaan was reduced to the small city of Bezek. Because of the city's insignificance, he did not receive the official title of king, but merely the local designation of lord [אלשיך].
Realizing his city has fallen, the ruler attempts to flee for his life [מלבי״ם]. However, the fighters of Judah capture him and cut off his thumbs and big toes [מצודת ציון, רד״ק].
This severe action carries several explanations. On a practical level, the mutilation serves to humiliate the defeated leader and completely remove his ability to physically resist [ביאור שטיינזלץ]. It is also meant to strike deep fear into the remaining Canaanite kings, deterring them from going to war against the Israelites [רלב״ג]. Taking a different perspective, the act serves as a symbolic punishment for the ruler's cowardice. As a leader, he was expected to fight bravely or die in battle, rather than escape to live in disgrace. Therefore, his hands are cut off because he failed to fight with them, and his feet are removed because he used them to run away from the battlefield [אברבנאל].
A deeper layer of understanding points to a divine reason behind the event. Subjecting an enemy to such suffering and mutilation actually contradicts the Israelites' rules of war, which dictate that enemy nations should be killed by the sword without inflicting unnecessary agony [מלבי״ם, אלשיך]. The fighters of Judah treat Adoni-bezek this way, unlike any of their other enemies, because God places the idea directly into their minds. God guides this specific outcome to punish the ruler measure for measure for his own past cruelty. It is a divine retribution that the defeated ruler himself recognizes, justifies, and accepts immediately [רלב״ג, מלבי״ם, אלשיך].