Albert Barnes Commentary Job 18:9

"A gin shall take [him] by the heel, [And] a snare shall lay hold on him." — Job 18:9 (ASV)

The gin – Another method of capturing wild animals. It was a snare made to spring suddenly on an animal, securing it by the neck or feet. We use a trap for the same purpose. The Hebrew word (פח pach) may denote anything of this kind – a snare, net, noose, and so on with which birds or wild animals are caught.

By the heel – By the foot.

And the robber shall prevail – He will be overpowered by the highwayman, or the plunderer will make a sudden descent upon him and strip him of all he has. The meaning is that destruction would suddenly overtake him. There can be no doubt that Bildad meant to apply all this to Job.