‘And all the men of Israel rose up out of their place, and put themselves in array at Baaltamar.'
These men who ‘rose up out of their place' were probably a large force lying in ambush. As the fleeing Israelites came towards them, followed by the exultant Benjaminites, they rose up and drew up in battle formation at Baaltamar, a place on the route. (Tamar means ‘palm tree'). Possibly it was a grove of palm trees where Baal worship had been prominent.
‘And the liers in wait of Israel broke out from their place, even from Maareh-geba (‘the meadow of Gibeah' - see Judges 20:10 for Gibeah as Geba).'
Totally unknown to the Benjaminites a hidden force began to advance on Gibeah from the rear. The writer is building up the picture of the battle as it progressed.