The most common and most likely answer to this crossword clue is the 7 plus 5 letter word COLONEL BOGEY
I've seen this crossword clue in The Guardian
C
O
L
O
N
E
L
B
O
G
E
Y
Buddy explains!
The straight part
We know that "an average player" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case an average player = colonel bogey.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.