The most common and most likely answer to this crossword clue is the 5 letter word PARRY
P
A
R
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Y
More clues leading to the result PARRY
Buddy explains!

The straight part
We know that "Duck" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case duck = parry.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 PARRY mean?
PARRY noun- A defensive or deflective action; an act of parrying.
- A simple defensive action designed to deflect an attack, performed with the forte of the blade.
- (combat sports and martial arts) A defensive move intended to change the direction of an incoming strike to make it miss its intended target, rather than block and absorb it; and typically performed with an open hand in a downward or sideways slapping motion.
- To avoid, deflect, or ward off (an attack, a blow, an argument, etc.).