The humiliation is more than only the defeat in battle. King Amaziah is taken prisoner, Jerusalem cannot keep out Jehoash, and part of the city wall gets demolished. An interesting detail is that Jehoash demolishes the part of the city wall that opens up in the direction of Samaria, which gives the humiliating message that Jerusalem lies open for Samaria.
13 And Jehoash king of Israel captured Amaziah king of Judah, the son of Jehoash, son of Ahaziah, at Beth-shemesh, and came to Jerusalem and broke down the wall of Jerusalem for four hundred cubits, from the Ephraim Gate to the Corner Gate.