How is it possible to declare a person Cheirem?
Rashi: It refers to one's Avadim and Shefachos Cana'anim.
What is this Pasuk coming to teach us?
Rashi and Ramban #1 (citing Erchin, 6b): It is teaching us that if Reuven, who has been sentenced to death at the hand of Beis-Din, is being taken out to be killed, and Shimon declares 'Erko alai!', his declaration is ineffective.
Ramban #2 (citing Erchin, 6b) and Rashbam: It teaches us that a person who has been sentenced to death by Beis-Din cannot be redeemed.
Ramban #3: With reference to a declaration by the Jewish army that in the event that Hashem delivers the enemy into their hands, they will be Machrim their cities, 1 this does not mean that all the contents, including the inhabitants, should be given to the Kohanim (or should be Hekdesh), 2 but that the entire town must be destroyed and all that it contains, Asur be'Hana'ah. 3
Ramban #4 (citing Raboseinu): It is La'av she'bi'Kelalus, 4 incorporating all of the above, in addition to placing the death-penalty upon someone who transgresses a Cheirem imposed by the Beis-Din ha'Gadol or by the king. 5
Ramban: Because the Din of Cheirem as regards Adam, only applies to Avadim who are his personal property, but not to people who are not. In fact, this was the mistake that Yiftach made, in thinking that the Neder that he made declaring the first one to come and greet him after his victory would be Hekdesh, pertained to his daughter as well (See Ramban DH 've'Zeh' and 've'Al Tihyeh'..
Ramban: Since that is obviously what they meant.
Ramban: As we find in the case of Yonasan, son of Shaul, whose father initially sentenced him to death for contravening the Cheirem that he had imposed upon the army - See Shmuel 1. 14:45.
What does "Mos Yumas" mean?