Jamieson, Fausset and Brown on Job 17:5

5. The Hebrew for "flattery" is "smoothness"; then it came to mean a prey divided by lot, because a smooth stone was used in casting the lots (De 18:8), "a portion" (Ge 14:24). Therefore translate, "He that delivers up his friend as a prey (which the conduct of my friends implies that they would do), even the eyes," &c. [Noyes] (Job 11:20). Job says this as to the sinner's children, retorting upon their reproach as to the cutting off of his (Job 5:4; 15:30). This accords with the Old Testament dispensation of legal retribution (Ex 20:5).