9 Joab saw that there were battle lines in front of him and behind him; so he selected some of the best troops in Israel and deployed them against the Arameans.

Read 2 Samuel 10:9 Using Other Translations

When Joab saw that the front of the battle was against him before and behind, he chose of all the choice men of Israel, and put them in array against the Syrians:
When Joab saw that the battle was set against him both in front and in the rear, he chose some of the best men of Israel and arrayed them against the Syrians.
When Joab saw that he would have to fight on both the front and the rear, he chose some of Israel’s elite troops and placed them under his personal command to fight the Arameans in the fields.