The Ammonites came out and drew up in battle formation at the entrance to their city, while the kings who had come were by themselves in the open country.
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.
He put the rest of the men under the command of Abishai1 his brother, and they were deployed against the Ammonites.
References for 1 Chronicles 19:11
Joab said, "If the Arameans are too strong for me, then you are to rescue me; but if the Ammonites are too strong for you, then I will rescue you.