Albert Barnes Commentary Jeremiah 48:45

"They that fled stand without strength under the shadow of Heshbon; for a fire is gone forth out of Heshbon, and a flame from the midst of Sihon, and hath devoured the corner of Moab, and the crown of the head of the tumultuous ones." — Jeremiah 48:45 (ASV)

Because of the force - Rather, without force. Translate it: “The fugitives have stood (that is, halted) powerless in the shadow of Heshbon.” As Heshbon was the capital of the Ammonites, the sense is that the defeated Moabites looked to Ammon for protection.

But afire ... - Not only will Ammon refuse aid to Moab, but her ruin is to come out from Heshbon. To show this, Jeremiah turns to the old triumphal poetry of the Mosaic age (marginal reference).

The corner - that is, of the beard... the crown of the head. The fire of war consumes both far and near, both hair and beard, that is, everything that it can singe and destroy.

The tumultuous ones - literally, “sons of the battle-shout,” the brave Moabite warriors.