The most common and most likely answer to this crossword clue is the 16 letter word QUARTER-FINALIST
I've seen this crossword clue in The Guardian
Q
U
A
R
T
E
R
-
F
I
N
A
L
I
S
T
Buddy explains!
The straight part
We know that "One of 8 left" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one of 8 left = quarter-finalist.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.