The most common and most likely answer to this crossword clue is the 11 letter word SELF-WILLED
I've seen this crossword clue in The Times
S
E
L
F
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W
I
L
L
E
D
Buddy explains!
The straight part
We know that "Stubborn" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case stubborn = self-willed.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 SELF-WILLED mean?
SELF-WILLED adjective- Obstinate; strong-minded; unyielding to the desires, concern or opinions of others.
- Possessing self-will; determined to pursue one's own desires or adhere to one's own opinion..