Boy singer with his rector for excitement (9)
I believe the answer is:
Here is my best explanation:
'boy singer' is the definition.
(I've seen this before)
'with his rector for excitement' is the wordplay.
'with' says to put letters next to each other.
'for excitement' indicates an anagram (I've seen this in other clues).
'his'+'rector' is 'hisrector'.
'hisrector' with letters rearranged gives 'CHORISTER'.