The most common and most likely answer to this crossword clue is the 13 letter word COUNTERATTACK
I've seen this crossword clue in The Guardian
C
O
U
N
T
E
R
A
T
T
A
C
K
Buddy explains!
The straight part
We know that "Retaliation" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case retaliation = counterattack.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 COUNTERATTACK mean?
COUNTERATTACK noun- An attack made in response to an attack by the opponents
- To attack in response to an attack by opponents