Albert Barnes Commentary Joshua 11:6

"And Jehovah said unto Joshua, Be not afraid because of them; for to-morrow at this time will I deliver them up all slain before Israel: thou shalt hock their horses, and burn their chariots with fire." — Joshua 11:6 (ASV)

Hamstring their horses – that is, cut the sinews of their hind hooves. This sinew, once severed, cannot be healed, and the horses would thus be irreparably lamed. This is the first appearance of horses in the wars with the Canaanites (Deuteronomy 17:16 and note).