Charles Ellicott Commentary 2 Samuel 11:21

"who smote Abimelech the son of Jerubbesheth? did not a woman cast an upper millstone upon him from the wall, so that he died at Thebez? why went ye so nigh the wall? then shalt thou say, Thy servant Uriah the Hittite is dead also." — 2 Samuel 11:21 (ASV)

Who struck down Abimelech? —See Judges 9:53. Joab anticipated David’s anger at his apparent rashness, and charged the messenger, if he were to observe it, to mention Uriah’s death. This was not likely to awaken any suspicion in the messenger, as it would appear to him rather as an effort on Joab’s part to throw the blame from himself upon Uriah as the leader of the assaulting party. The messenger appears to have told all in one breath, so that there was no opportunity for David to express displeasure. The reference to the case of Abimelech shows how familiar the Israelites were with the past history of their people.