The double use of the verb march down
suggests that the people “had largely retreated into the hill country and now had to descend to the battlefield in the valley of the Kishon. One might think that it refers to the descent from Mount Tabor at the moment of attack (Judges 4:14), but Tabor is not mentioned here. Furthermore, since the tribes spoken of here are contrasted with those who did not join the fighting, it is unlikely that a particular moment of the battle was being spoken of."1
13 Then down marched the remnant of the noble; the people of the LORD marched down for me against the mighty.