The Chidush of Rav Engel is that the Targum Yonasan on Devarim 22:26 agrees with the opinion of Avuha d'Shmuel in Kesuvos 51b, even though the Halachah does not follow Avuha d'Shmuel.

1) Avuha d'Shmuel maintains that if the wife of a Yisrael was raped, this renders her forbidden to her husband because we are concerned that in the end she may have consented (the Halachah follows Rava who maintains that even if she did consent, this is only because of the Yetzer ha'Ra, but it is not considered full consent and therefore she remains permitted to her husband, unless he is a Kohen).

2) The Targum Yonasan (Devarim 22:26) translates the first part of the verse, referring to rape, in the standard way -- namely, that you should not do anything to the girl for she is not liable to the death penalty. However, the Targum adds "but her husband must release her with a Get." Rav Engel writes that this conforms with the opinion of Avuha d'Shmuel (he disagrees with the explanation given by the commentary on the Targum Yonasan printed in the Chumashim).

3) Rav Engel adds that the Targum Yonasan also does not agree with Tosfos in Zevachim 2b, DH Stam, who writes that if a wife was unfaithful, the husband is not actually obligated to divorce her but they are merely forbidden to have relations. If the Targum would have agreed with Tosfos it would have been sufficient to say that she is forbidden to her husband. It would not have been necessary to write that he must divorce her with a Get.

Kol Tuv,

Dovid Bloom