The most common and most likely answer to this crossword clue is the 9 plus 8 letter word ANECDOTAL EVIDENCE
I've seen this crossword clue in The Daily Telegraph
A
N
E
C
D
O
T
A
L
E
V
I
D
E
N
C
E
Buddy explains!
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.