Albert Barnes Commentary Judges 15:8

"And he smote them hip and thigh with a great slaughter: and he went down and dwelt in the cleft of the rock of Etam." — Judges 15:8 (ASV)

Hip and thigh - A proverbial expression of doubtful origin, meaning all the "great" and "mighty," all the choice pieces like the thigh and shoulder.

In the top of the rock - Rather, "the cleft of the rock." These clefts of the rock were the natural fortresses and hiding places of the land. (Isaiah 2:21; Isaiah 57:5. Compare to 1 Samuel 13:6; 1 Kings 18:13.)

Etam - Not the same as the place in the territory of Simeon (1 Chronicles 4:32). Its situation is uncertain, but a site near Eleutheropolis ("Beth-jibrin") is required; and there exist some extraordinary caverns in the soft limestone or chalky rock, fifteen or twenty feet deep, with perpendicular sides, opening into extensive excavations in the rock, about two hours from Eleutheropolis. (Conder conjectures it to be the same as Atab, a village 12 miles southwest of Jerusalem, in the ‛arkub or Ridge.)