Charles Ellicott Commentary 2 Samuel 18:14

"Then said Joab, I may not tarry thus with thee. And he took three darts in his hand, and thrust them through the heart of Absalom, while he was yet alive in the midst of the oak." — 2 Samuel 18:14 (ASV)

I may not tarry thus. —Joab evidently feels the pointed arguments made by the man, but, determined on his act of violence, he sees that it is worse than useless to delay further. His act was simply murder. In a lawless age, it was defensible as the one act that terminated the rebellion, made a renewal of it impossible, and destroyed a traitor and would-be parricide who was likely otherwise to escape punishment; but it was a distinct disobedience of express orders, and Joab’s taking the execution into his own hands was willful and deliberate murder.

Three darts. —The word means a rod or staff. Also, the word heart is the same as the following word midst, and is therefore not to be taken too literally. Joab seized such sticks as were at hand in the wood and thrust them into Absalom, giving him most painful and probably mortal wounds, but not instantly killing him. Then (2 Samuel 18:15) the ten men who had Joab’s armour and weapons came up and finally killed Absalom.