Albert Barnes Commentary 2 Kings 9:11

"Then Jehu came forth to the servants of his lord: and one said unto him, Is all well? wherefore came this mad fellow to thee? And he said unto them, Ye know the man and what his talk was." — 2 Kings 9:11 (ASV)

This mad fellow—The captains, seeing his excited look, his strange action, and his extreme haste, call him (as soldiers would) “this wild fellow.”