II Samuel - Chapter 2
Things Get Out of Hand
G-d instructed David to go to Hebron, which was in the territory of Judah. There, the Tribe of Judah anointed him and crowned him king over them. David heard how the people of Yaveish-Gilad recaptured Shaul's remains and gave them a proper burial. David blessed the people of Yaveish-Gilad and promised them his support. But Shaul's general Avner took Shaul's surviving son, Ishboshes, and made him king in Shaul's place. He started gradually, with Ephraim and Benjamin, until Ishboshes eventually reigned over all of Israel except for Judah. Ishboshes reigned for two years; David was king in Judah for seven years. It is unclear from the text whether Ishboshes' two years fell at the beginning, middle or end of David's seven.
(A brief diversion: Avner was a tremendous Torah scholar. He supported Ishboshes not because he insisted on pursuing a lost cause, but because he felt it was the will of G-d. The Torah tells us in Genesis 35:11 that kings (plural) were destined to be born from Jacob. At that time, all the founders of the Tribes were born except for Benjamin. Avner inferred that a minimum of two Benjaminite kings were foretold by this verse. He therefore believed that Ishboshes was the rightful king, at least temporarily.)
Now, here's where things spun wildly out of control. Avner was out with Ishboshes' army. They came to a pool of water, with Yoav and David's men on the other side. Avner challenged Yoav's men to a duel, presumably just fencing for sport. But things got out of hand and the fighting escalated far beyond mere sport. Soon, a full-scale battle broke out between the two forces. Yoav's brother Asahel started chasing Avner. Avner asked him to stop or he would be forced to defend himself. Asahel refused to break off his pursuit, so Avner dealt him a fatal blow, carefully executed by the fifth rib. Yoav and his other brother, Avishai, pursued Avner, but they were unable to capture him. Avner called out to Yoav that things had gone too far; Yoav replied that Avner never should have started with the whole idea of a duel. Nevertheless, Yoav called off his men. David's army lost 19 men, plus Asahel. The army of Ishboshes, however, had 360 casualties. To make matters even worse, the two factions were now at war.