The most common and most likely answer to this crossword clue is the 12 letter word MIDDLEWEIGHT
I've seen this crossword clue in The Daily Telegraph
M
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More clues leading to the result MIDDLEWEIGHT
Buddy explains!
The straight part
We know that "boxer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case boxer = middleweight.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 MIDDLEWEIGHT mean?
MIDDLEWEIGHT noun- A weight class in professional boxing between light middleweight or welterweight and super middleweight or cruiserweight; a similar division in wrestling and other sports
- A boxer who fights in this division; a similar wrestler etc
- (by extension) An employee ranking anywhere between junior and senior.