The most common and most likely answer to this crossword clue is the 8 plus 6 letter word STANDARD BEARER
I've seen this crossword clue in Independent
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More clues leading to the result STANDARD BEARER
Buddy explains!
The straight part
We know that "Outstanding leader/but one below par?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case outstanding leader/but one below par? = standard bearer.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 STANDARD BEARER mean?
STANDARD BEARER noun- A person who carries a flag or banner (a standard).
- A person who visibly leads.