John Gill Commentary 2 Chronicles 13:15

"Then the men of Judah gave a shout: and as the men of Judah shouted, it came to pass, that God smote Jeroboam and all Israel before Abijah and Judah." — 2 Chronicles 13:15 (ASV)

Then the men of Judah gave a shout
Taking heart at the sound of the trumpets, and in order to encourage one another, and intimidate the enemy; (See Gill on 1 Samuel 17:20),

and as the men of Judah shouted, it came to pass, that God smote
Jeroboam and all Israel before Abijah and Judah ;
possessed them with a panic, so that they fled at once, as follows.