The most common and most likely answer to this crossword clue is the 10 letter word DISSIDENTS
I've seen this crossword clue in The Daily Telegraph
D
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D
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More clues leading to the result DISSIDENTS
Buddy explains!

The straight part
We know that "rebels" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rebels = dissidents.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 DISSIDENTS mean?
DISSIDENTS noun- A person who formally opposes the current political structure, the political group in power, the policies of the political group in power, or current laws.
- One who disagrees or dissents; one who separates from the established religion.