The most common and most likely answer to this crossword clue is the 12 letter word RECALCITRANT
I've seen this crossword clue in The Daily Telegraph
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More clues leading to the result RECALCITRANT
- Mostly remember tirade about citation that’s perverse
- Tartan cleric, unruly and defiant
- Deny penning revolutionary piece, almost defiant
- Defiant bluster undermining cleric at broadcast
- Obstinate article penned by unusually tart cleric
- Clatter in car turns out hard to handle
- Being obstinate, managed to stop extremely curt article being rewritten
- Stubborn Republican about to block review of Tennessee report
Buddy explains!

The straight part
We know that "Obstinate" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case obstinate = recalcitrant.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.
Crossword Answer definitions
RECALCITRANT noun- A person who is recalcitrant.
- Marked by a stubborn unwillingness to obey authority.
- Unwilling to cooperate socially.
- Difficult to deal with or to operate.
- (of seed, pollen, spores) Not viable for an extended period; damaged by drying or freezing.