Charles Ellicott Commentary 2 Samuel 2:19

"And Asahel pursued after Abner; and in going he turned not to the right hand nor to the left from following Abner." — 2 Samuel 2:19 (ASV)

Asahel pursued after Abner. —Asahel, the youngest of David’s three nephews, took part in the battle with his elder brothers. Knowing full well how completely Ish-bosheth’s cause depended on Abner, he persistently sought him out in the pursuit. His great swiftness enabled him to overtake Abner and, coming behind him, endanger his life.

Abner was unwilling to injure him, and only after remonstrating with him and urging him to seek the spoil of some warrior more nearly his equal (2 Samuel 2:20–22), did he unwillingly slay him “with the butt end of his spear.” Spears were sharpened at the butt end for the purpose of sticking them into the ground (1 Samuel 26:7). Abner’s reluctance to kill Asahel may have been partly due to his extreme youth, but was chiefly through dread of Joab’s vengeance (2 Samuel 2:22).

The phrase “the fifth rib,” here and wherever else it occurs (2 Samuel 3:27; 2 Samuel 4:6; 2 Samuel 20:10), should be translated as abdomen.