1)
Who left the city?
1.
Rashi: The ambush, who set the city on fire.
2)
Why does it say "Likrasam"?
1.
Malbim: Anshei Ai wanted to flee to the city (and the ambush came out towards them).
3)
What is the meaning of "l'Yisrael ba'Tavech"?
1.
Malbim: Yisrael surrounded them on all four sides