| Clarke's Commentary on the Bible In the fifth rib - I believe חמש chomesh, which we render here and elsewhere the fifth rib, means any part of the abdominal region. The Septuagint translate it την ψοαν, the groin; the Targum, the right side of the thigh, i.e., (the phrase of the Targumist being interpreted), the privy parts. That it means some part of the abdominal region, is evident from what follows, And shed out his bowels to the ground. It appears from this that, in plain English, he ripped up his belly.
Gill's Exposition of the Entire BibleBut Amasa took no heed to the sword that was in Joab's hand,.... In his left hand, for with his right hand he took him by the beard; he might see the sword drop out of the scabbard, and Joab take it up, which he supposed he did in order to put it into its sheath again, having no suspicion of his wicked design, and therefore not at all upon his guard to prevent it: so he smote him therewith in the fifth rib; in the same place where Abner smote Asahel, and Joab Abner; See Gill on 2 Samuel 2:23 and See Gill on 2 Samuel 3:27, he must strike him, as some observe, on the left side, because he was embracing him; and the stroke must be deadly, because he struck him in the pericardium, which surrounds the heart round with water, to refrigerate it; for the lower part of the heart reaches to the fifth rib; see John 19:34 (u): and shed out his bowels to the ground; which fell out through the incision made by the sword: and struck him not again: he gave him such a home thrust, there was no need to repeat it, he dispatched him at once: and he died; and thus, though he was pardoned by David, and promoted to honour by him, yet the providence of God would not suffer him to go unpunished for joining with Absalom in an unnatural rebellion against his uncle: so Joab and Abishai his brother pursued after Sheba the son of Bichri: for Amasa being slain, Joab without any ceremony reassumed his post as general, and, with his brother Abishai under him, made all the haste they could in pursuit of the rebel. (u) Weemse's Portrait of Man, p. 25.
Geneva Study BibleBut Amasa took no heed to the sword that was in Joab's hand: so he smote him therewith in the fifth rib, and shed out his bowels to the ground, and struck him not again; and he died. So Joab and Abishai his brother pursued after Sheba the son of Bichri.
Wesley's Notes 20:10 The sword - Which falling out, as it seemed, casually, he supposed that Joab intended only to put it into its scabbard, and therefore took no care to defend himself against the stroke. So Joab - Who now boldly resumed his former place, and marched in the head of the army. It is not strange, that Amasa's soldiers did not fight to revenge his death; partly, because not many of them were yet come up, as the following verse s shew; and partly, because Joab's interest and authority with the military - men was very great; especially, with David's guards, who were here present, and who had no kindness for Amasa, as having been the general of the rebellious army; and, as they might think, not fit to be put into a place of so great trust.
King James Translators' Notesstruck...: Heb. doubled not his stroke
Jamieson-Fausset-Brown Bible Commentary2Sa 20:10-13. Amasa Is Slain. 10. smote him . in the fifth rib-the seat of the liver and bowels, where wounds are mortal. struck him not again-that is, despatched him at the first blow.
Matthew Henry's Concise Commentary20:4-13 Joab barbarously murdered Amasa. The more plot there is in a sin, the worse it is. Joab contentedly sacrificed the interest both of the king and the kingdom to his personal revenge. But one would wonder with what face a murderer could pursue a traitor; and how, under such a load of guilt, he had courage to enter upon danger: his conscience was seared. | 
