1)
Why did they need to strike them? Verse 11 implies that Hashem struck them, and Yisrael did not need to fight!
1.
Malbim: They fought only the cities around Grar, which are of the Pelishtim; Hashem did not strike them. Yisrael struck them, for they feared Yisrael.
2)
Why does it say "va'Yavozu? Vizah"? Verse 12 called the spoils "Shalal"!
1.
Malbim (12 and Yeshayah 8:1): Shalal is what remains automatically when the enemy falls in war. It is called Bizah only when plunderers take it.
