返り討ちに遭う

kaeriuti ni au
to challenge someone, only to have it end in certain defeat

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This seems like a difficult concept to transliterate, briefly, into English. Briefly is the key notion for me, because lately I am working under tight restrictions in line lengths and cannot be verbose. I forget the full original Japanese sentence, but I could not have ended the English with:

you're going to challenge them only to have it end in your certain defeat.

That would have been too long. I think I maintained the sense of the original when I pared it down to:

you'll end in certain defeat.

...within the context of the sentence and the surrounding story, which was indicating that the second person was going to challenge something formidable.