Jamieson, Fausset and Brown on Judges 4:15

15. the Lord discomfited Sisera--Hebrew, "threw his army into confusion"; men, horses, and chariots being intermingled in wild confusion. The disorder was produced by a supernatural panic (see on Jud 5:20).

so that Sisera lighted down off his chariot, and fled away on his feet--His chariot being probably distinguished by its superior size and elegance, would betray the rank of its rider, and he saw therefore that his only chance of escape was on foot.