1)
Here it says that they will fall "Al Pnei ha'Sadeh." The previous verse said that they will fall on the mountains!
1.
Radak: When they will be in the field or on the mountains, all will fall to the sword and other punishments.
2.
Malbim: When they descend from the mountains, Hashem will strike all who come against Yerushalayim with a plague.
