Boy in church worried his rector (9)
I believe the answer is:
chorister
'boy in church' is the definition.
(boy in a choir)
'worried his rector' is the wordplay.
'worried' indicates an anagram.
'his'+'rector'='hisrector'
'hisrector' anagrammed gives 'CHORISTER'.
(Other definitions for chorister that I've seen before include "Boy singing" , "Choirboy or girl" , "Boy in church" , "Church, cathedral singer" , "Choir member" .)