Isaiah 31:8

Then shall the Assyrian fall with the sword, not of a
mighty man
That is, the Assyrian army under Sennacherib their king, which besieged Jerusalem in Hezekiah's time; which, as soon as the people were brought to a sense of their sin, and repentance for it, and cast away their idols as a proof of it, were utterly destroyed; but not in battle, not by the sword of Hezekiah, or any of his valiant generals:

and the sword, not of a mean man, shall devour him;
neither the sword of a general, nor of a private soldier, nor indeed of any man, but of an angel; see ( 2 Kings 19:35 ) :

but he shall flee from the sword;
from the drawn sword of the angel, who very probably appeared in such a form as in ( 1 Chronicles 21:16 ) which Sennacherib king of Assyria seeing, as well as the slaughter made in his army by him, fled from it; in the Hebrew text it is added, "for himself" ^F25; he fled for his life, for his own personal security; see ( 2 Kings 19:36 ) :

and his young men shall be discomfited;
his choice ones, the flower of his army: or "melt away" ^F26, through fear; or die by the stroke of the angel upon them: the sense of becoming "tributary" seems to have no foundation.