Why will Hashem be like a Shachal (young lion) to them?
Radak: Since they forgot Me, I will abandon them and hand them over to the nations.
Malbim: They forgot Hashem's good and denied it, but the evil that comes to them, they attribute it to Hashem. Hashem appears to them like an evil tearing beast - a Shachal, tiger, bear or Lavi (mature lion) (8). This and the coming verse mention four Chayos corresponding to the four kingdoms that destroyed them. Shachal is Malchus Bavel and Ashur. The first beast that Daniel saw was a lion, like I explained above from "Acharei Hashem Yelechu k'Aryeh Yish'ag" (refer to 11:10:1:4).
What is the significance of "[k'Namer] Al Derech Ashur"?
Rashi: Every Ashur in Tanach has a Dagesh [in the Shin], except for this, for it is not the name of a place. Rather, I will ambush and guard, like "Ashurenu v'Lo Karov" (Bamidbar 24:17). Radak - lions and tigers wait, ready to tear what passes on the road. So I made their enemies rule over them, and they had no strength to save themselves, until they returned to Me and I had mercy on them. Ashur is Pa'ul conjugation. This is like "v'Ishru b'Derech Binah" (Mishlei 9:6); that has the grammatical form of Shimru and Zichru.
Malbim: Namer is Malchus Yavan. It came "Al Derech Ashur" - it did not exile them from their land, "Namer Shoked Al Areihem" (Yirmeyah 5:6).
