1)
What is the meaning of "va'Yimshoch ha'Orev"?
1.
Rashi #1: They blew the Shofar [and extended the sound]. Radak - this is like "bi'Mshoch ha'Yovel" (Shemos 19:13).
2.
Rashi #2: Through the Shofar, the ambush drew the camp with it to the city.
3.
Radak based on Targum Yonasan: It is Po'el Omed; the ambush itself drew close to the city.