Tafsir of Al-Anfal 8:15

{زحفا} (In a body/crawling): This is a circumstantial qualifier (ḥāl) for "those who disbelieve."

• The Zaḥf: It is the massive army that, due to its sheer size, appears to be "crawling" (yazḥafu)—that is, moving slowly, like a child crawling on its buttocks. It is named using the verbal noun (maṣdar). Its plural is zuḥūf.
• The Meaning: When you encounter them for battle, and they are numerous while you are few, do not flee—let alone if you are equal or superior in number.
• Alternative Interpretations: It may be a circumstantial qualifier for both groups (i.e., when you meet them, both you and they are "crawling" toward each other). Or, it may refer to the believers, as if they were being warned of what would happen on the day of Hunayn when they turned their backs in retreat, despite being a "crawling" force of twelve thousand. The preceding verse serves as a prohibition against fleeing on that day.

{ومن يولهم يومئذ دبره} (And whoever turns his back to them on that day): This is a sign of that [prohibition].

{إلا متحرفا لقتال} (Except to maneuver for battle): This is the act of attacking after retreating, making the enemy believe one is defeated, then turning back upon them. It is a tactic of war and its stratagems.

{أو متحيزا إلى فئة} (Or to join a company): That is, withdrawing to another group of Muslims, other than the one he is currently with.

• From Ibn Umar (may Allah be pleased with him): "I went out with a military expedition, and they fled. When they returned to Medina, they were ashamed and hid in their homes. I said, 'O Messenger of Allah, we are the fugitives.' He replied, 'No, you are the ones who return to fight (al-akkārūn), and I am your company (fi'ah).'"
• From the Battle of al-Qadisiyyah: A man fled and came to Medina to Umar (may Allah be pleased with him) and said, "O Commander of the Faithful, I am ruined; I fled from the zaḥf." Umar replied, "I am your company."
• From Ibn Abbas (may Allah be pleased with him): "Fleeing from the zaḥf is among the greatest of major sins."

Grammatical Note: If you ask, "What governs the accusative case of illā mutaḥarrifan?" I say: It is a circumstantial qualifier (ḥāl), and the illā is redundant. Or, it is an exception from those who turn their backs; meaning: "Whoever turns their back to them, except for a man among them who is maneuvering or joining a company."

• Recitation: Al-Hasan read dubrahu with a sukūn (on the bā').
• Morphology: The weight of mutaḥayyiz is mutaftiʿil, not mutafaʿʿil, because it is derived from ḥāza-yaḥūzu. Thus, the mutafaʿʿil form would be mutaḥawwiz.