The most common and most likely answer to this crossword clue is the 13 letter word KAPELLMEISTER
I've seen this crossword clue in The Daily Telegraph
K
A
P
E
L
L
M
E
I
S
T
E
R
Buddy explains!
The straight part
We know that "Church leader" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case church leader = kapellmeister.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 KAPELLMEISTER mean?
KAPELLMEISTER noun- A leader or conductor of a musical group such as an orchestra.
- A term used during the baroque and classical period for the person in charge of music at a noble court.