The gin shall take him by the heel, and the robber shall prevail against him.

Jamieson-Fausset-Brown Bible Commentary

9. robber-rather answering to "gin" in the parallel clause, "the noose shall hold him fast" [Umbreit].

Matthew Henry's Concise Commentary

18:5-10 Bildad describes the miserable condition of a wicked man; in which there is much certain truth, if we consider that a sinful condition is a sad condition, and that sin will be men's ruin, if they do not repent. Though Bildad thought the application of it to Job was easy, yet it was not safe nor just. It is common for angry disputants to rank their opponents among God's enemies, and to draw wrong conclusions from important truths. The destruction of the wicked is foretold. That destruction is represented under the similitude of a beast or bird caught in a snare, or a malefactor taken into custody. Satan, as he was a murderer, so he was a robber, from the beginning. He, the tempter, lays snares for sinners wherever they go. If he makes them sinful like himself, he will make them miserable like himself. Satan hunts for the precious life. In the transgression of an evil man there is a snare for himself, and God is preparing for his destruction. See here how the sinner runs himself into the snare.