The most common and most likely answer to this crossword clue is the 8 letter word REVENGED
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Buddy explains!

The straight part
We know that "fought back" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fought back = revenged.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does REVENGED mean?
REVENGED verb- To take revenge for (a particular harmful action) or on behalf of (its victim); to avenge.
- To take one's revenge (on or upon someone).
- To take vengeance; to revenge itself.