The most common and most likely answer to this crossword clue is the 10 letter word STREAKIEST
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Buddy explains!

The straight part
We know that "most uneven in quality" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case most uneven in quality = streakiest.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
STREAKIEST adjective- Having streaks.
- Used to describe a shot where the ball deflects off the edge of the bat, but is not caught by the slips or wicket-keeper and instead results in runs for the batsman.
- (chiefly of a person, usually North America) Having alternating periods of good and bad performances; inconsistent.
- Not well-executed, due to luck more than skill.