Carl Friedrich Keil and Franz Delitzsch Old Testament Commentary

Jephthah expressed to the elders his astonishment that they had formerly hated and expelled him, and now came to him in their distress, sc., to make him their leader in time of war. Thus he lays his expulsion upon the shoulders of the elders of Gilead, although it was only by his brethren that he had been driven away from his father's house, inasmuch as they had either approved of it, or at all events had not interfered as magistrates to prevent it. We cannot indeed infer from this reproach, that the expulsion and disinheriting of Jephthah was a legal wrong; but so much at all events is implied, namely, that Jephthah looked upon the thing as a wrong that had been done to him, and found the reason in the hatred of his brethren. The Mosaic law contained no regulation upon this matter, since the rule laid down in Deu 21:15-17 simply applied to the sons of different wives, and not to a son by a harlot.