Who left the city?
Rashi: The ambush, who set the city on fire.
Why does it say "Likrasam"?
Malbim: Anshei Ai wanted to flee to the city (and the ambush came out towards them).
What is the meaning of "l'Yisrael ba'Tavech"?
Malbim: Yisrael surrounded them on all four sides