C. F. Keil and Franz Delitzsch on 2 Samuel 4:1

Murder of Ishbosheth. - 2Sa 4:1. When the son of Saul heard of the death of Abner, “his hands slackened,” i.e., he lost the power and courage to act as king, since Abner had been the only support of his throne. “And all Israel was confounded;” i.e., not merely alarmed on account of Abner’s death, but utterly at a loss what to do to escape the vengeance of David, to which Abner had apparently fallen a victim.