Charles Ellicott Commentary 1 Chronicles 18:4

"And David took from him a thousand chariots, and seven thousand horsemen, and twenty thousand footmen; and David hocked all the chariot horses, but reserved of them for a hundred chariots." — 1 Chronicles 18:4 (ASV)

A thousand chariots, and seven thousand horsemen. —Hebrew text of Samuel, “a thousand and seven hundred horsemen.” The territory of Zobah lay somewhere in the great plain of Aram. Hadadezer would, therefore, be strong in chariots and horses, and our reading is probably correct. (Compare to 1 Chronicles 19:18.)

Houghed. — Hamstrung — i.e., cut the sinews of the hind legs, so as to disable them.

Chariot horses. —The same Hebrew term has just been rendered chariots. It also means chariot soldiers.

David reserved a hundred chariots, with their horses, probably for his own use. Horses were always a luxury in Israel. (Compare to Isaiah 2:7.) Solomon recruited his stud from Egypt. (Compare to the prohibition, Deuteronomy 17:16.)