1)
What is the meaning of "va'Yach Tzarav Achor"?
1.
Rashi: He struck [the Pelishtim] from the back (anus), with hemorrhoids.
2.
Radak #1: The Mezid sinners in Yisrael, He struck them until they went back in front of their enemies.
3.
Radak #2: Yisrael fled the Pelishtim, and the Pelishtim pursued them and struck them from the back.
2)
What was the eternal shame?
1.
Rashi: The hemorrhoids.
2.
Radak: The exile of the Aron.