John Gill Commentary 2 Samuel 2:25

"And the children of Benjamin gathered themselves together after Abner, and became one band, and stood on the top of a hill." — 2 Samuel 2:25 (ASV)

And the children of Benjamin gathered themselves together
after Abner
Either those that were with him before, who upon the battle were dispersed, but now got together again; or others of that tribe, who, hearing of the defeat of Abner, went out of the several cities after him, to strengthen his hands, and renew the fight with Joab:

and became one troop ;
were united together in a body, and became a regular troop:

and stood on the top of an hill ;
which was some advantage to them, and from whence they could take a view of Joab's army, and observe its motions.