The most common and most likely answer to this crossword clue is the 10 letter word POLEMICIST
I've seen this crossword clue in The Times
P
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L
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M
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More clues leading to the result POLEMICIST
Buddy explains!

The straight part
We know that "one likely to be controversial" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one likely to be controversial = polemicist.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 POLEMICIST mean?
POLEMICIST noun- A person who writes polemics
- A person who puts forward controversial views