The most common and most likely answer to this crossword clue is the 5 plus 10 letter word GREEN WOODPECKER
G
R
E
E
N
W
O
O
D
P
E
C
K
E
R
More clues leading to the result GREEN WOODPECKER
Buddy explains!
The straight part
We know that "Drummer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case drummer = green woodpecker.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.