Probably an allusion to the frantic efforts of the chariot-horses to disengage themselves from the morass (Judges 4:15 note).
Mighty ones - Applied to bulls Psalm 22:12 and horses Jeremiah 8:16; Jeremiah 47:3; Jeremiah 50:11; elsewhere, as probably here, to men.

Then were the horsehoofs broken - In very ancient times horses were not shod; nor are they to the present day in several parts of the East. Sisera had iron chariots when his hosts were routed; the horses that drew these, being strongly urged on by those who drove them, had their hoofs broken by the roughness of the roads; in consequence of which they became lame, and could not carry off their riders. This is marked as one cause of their disaster.

Then were the horse hoofs broken by means of the pransings,.... Either through the force of the waters of the river, where they pranced and plunged, and could have no standing; or through the swift haste they made to run away, striking the earth so quick, and with such force and vehemence, that their hoofs were broken thereby, especially on stony ground, and so their speed retarded:
the pransings of the mighty ones; either their riders, princes, and great personages, who made them prance, leap, and run with great speed and force; or horses strong and mighty, being such as were selected for this purpose, and trained to war.

Then were the horse hoofs broken by the means of the prancings--Anciently, as in many parts of the East still, horses were not shod. The breaking of the hoofs denotes the hot haste and heavy irregular tramp of the routed foe.

22 Then did the hoofs of the horses stamp
With the hunting, the hunting of his strong ones.
23 Curse ye Meroz, saith the angel of the Lord;
Curse ye, curse ye the inhabitants thereof!
Because they came not to the help of Jehovah,
To the help of Jehovah among the mighty.
24 Blessed before women be Jael,
The wife of Heber the Kenite,
Blessed before women in the tent!
The war-chariots of the enemy hunted away in the wildest flight (Judges 5:22). The horses stamped the ground with the continuous hunting or galloping away of the warriors. דהרה, the hunting (cf. דּהר, Nahum 3:2). The repetition of the word expresses the continuance or incessant duration of the same thing (see Ewald, 313, a.). אבּירים, strong ones, are not the horses, but the warriors in the war-chariots. The suffix refers to סוּס, which is used collectively. The mighty ones on horses are not, however, merely the Canaanitish princes, such as Sisera, as Ewald maintains, but the warriors generally who hunted away upon their war-chariots.

Horses hoofs - Their horses, in which they put most confidence, had their hoofs, which are their support and strength, broken, either by dreadful hail - stones, or rather, by their swift and violent running over the stony grounds, when they fled with all possible speed from God and from Israel. Pransings - Or because of their fierce or swift courses. Mighty ones - Of their strong and valiant riders, who forced their horses to run away as fast as they could.