וַיַּךְ־צָרָ֥יו אָח֑וֹר חֶרְפַּ֥ת ע֝וֹלָ֗ם נָ֣תַן לָֽמוֹ׃
And He smote His adversaries backward; He put upon them a perpetual reproach.
Rashi on Psalms
And He smote His adversaries from the rear Plagues of the rear with hemorrhoids, which is a disgrace of perpetual ridicule for them.