# Every stroke of the appointed rod that Yahweh will lay on them

Yahweh causing an army to defeat the Assyrians is spoken of as if Yahweh would hit the Assyrians with a rod. 

# will be accompanied

"the people of Judah will accompany it" 

# tambourines

This is a musical instrument with a head like a drum that can be hit and with pieces of metal around the side that sound when the instrument is shaken.

# he battles, waving his weapons, and fights with them

Yahweh causing the enemy army to defeat the Assyrians is spoken of as if Yahweh were a warrior who would fight along with the enemy army.