Adam Clarke on 2 Samuel 23:6

But the sons of Belial shall be all of them as thorns - There is no word in the text for sons; it is simply Belial, the good-for-nothing man, and may here refer - first to Saul, and secondly to the enemies of our Lord.

As thorns thrust away - A metaphor taken from hedging; the workman thrusts the thorns aside either with his bill or hand, protected by his impenetrable mitten or glove, till, getting a fair blow at the roots, he cuts them all down. The man is fenced with iron, and the handle of his bill is like the staff of a spear. This is a good representation of the dubbing-bill, with which they slash the thorn hedge on each side before they level the tops by the pruning-shears. The handle is five or six feet long. This is a perfectly natural and intelligible image.