What is "Achariso"?
Radak: It is his son. The same applies to "va'Achariso ba'Cherev Eherog" (Amos 9:1), "v'Lo l'Achariso" (Daniel 11:4).
Malbim: It is sons that come after him.
How will he be cut off?
Radak: No remembrance of him will remain.
What is "b'Dor Acher Yimach Shmam"?
Rashi 1 : After they are cut off, their name and fame will be wiped out. There will be no memory of them in the mouth of the generation born after his name is destroyed.
Radak: In the third generation, the name of the father and son will be wiped out. This is why it says "Shmam" (plural).
Malbim: There will be no remnant of them.
In some texts, this is at the end of Rashi on verse 11.
