John Gill Commentary Isaiah 30:31

"For through the voice of Jehovah shall the Assyrian be dismayed; with his rod will he smite [him]." — Isaiah 30:31 (ASV)

For through the voice of the Lord shall the Assyrian be
beaten down
As anything is by a storm of thunder, lightning, hail, and rain: or "fear", or be "affrighted", as the Vulgate Latin and Arabic versions render it; Sennacherib, the Assyrian monarch, and that part of his army which escaped, though not destroyed by it, were put into the utmost consternation: this shows that the prophecy in the context refers to the overthrow of the Assyrian army by the angel, when besieging Jerusalem in Hezekiah's time; though the Assyrian is sometimes used for any enemy of God's people at other times, particularly antichrist, and especially the eastern antichrist, the Turk:

[which] smote with a rod ;
other nations, particularly the Jews, whom the Assyrian is expressly said to smite with a rod; and because he was an instrument in God's hand for the chastising of that people, he is called the rod of his anger, (Isaiah 10:5Isaiah 10:24) but now he that smote shall be smitten himself; him whom God used as a rod to correct others, he will smite with his rod, for his own correction: for this may be understood of God, and be rendered thus, "with a rod, he", that is, God, "shall smite" the Assyrian, as before; so Aben Ezra and Kimchi. The Targum interprets the "rod" of dominion.