In some cases those who have their heads crushed are physically descended from Abraham, but by their actions they show themselves to be at enmity with those who are faithful to Yahweh. Like Cain, who was physically a seed of the woman but showed himself to be the seed of the serpent by killing his brother, Abimelech shows the lineage of his ethical character by killing seventy of his brothers (Judg 9:1–5; cf. also 9:34–49, where he slaughters his subjects [9:6]). Judgment falls on the seed of the serpent (Abimelech), however, when a woman throws a millstone on Abimelech’s head (rō’š) and his skull (gulěggōlet) is crushed (rāsas)(9:53).  - Dr. Jim Hamilton