The most common and most likely answer to this crossword clue is the 3 plus 4 letter word ALL STAR
I've seen this crossword clue in The Guardian
A
L
L
S
T
A
R
Buddy explains!
The straight part
We know that "second-raters excepted" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case second-raters excepted = all star.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 ALL STAR mean?
ALL STAR noun- A member of a team of star players.
- Of which all members or participants are celebrities.