Why does it say "ba'Yom ha'Hu"?
Radak: At the same time that Melech Ashur destroyed Egypt and Kush, afterwards he came to Yerushalayim and was stricken there.
How will they resemble women?
Radak: They will be weak like women due to the waving of Hashem's hand. I.e. this will be due to Hashem; they will not have strength to fight the enemy, like women.
Malbim: They are afraid of everything.
Why does it say "v'Charad u'Fachad Mipnei Tenufas Yad Hashem"?
Malbim: Charadah is sudden panic from a new blow. Pachad is fear that extends many days from something not in front of his eyes. Sometimes a person panics due to a small sudden mishap, but after he sees that it is small, he is not afraid. Sometimes he fears something without substance, for he mistakenly thought that it is a great matter that can harm him. After he sees that it is small, he will not fear it. Egypt's hearts will be so cowardly that due to the motion of Hashem's hand, i.e. a mere hint via His gesture, they will see it as a sign of evil, and panic and continue to fear, like women do.
