Musician's recital isn't ruined by tenor initially (12)
I believe the answer is:
clarinettist
'musician's' is the definition.
(clarinettist is a kind of musician)
'recital isn't ruined by tenor initially' is the wordplay.
'ruined' indicates anagramming the letters.
'by' means one lot of letters go next to another.
'initially' says to take the initial letters.
The first letter of 'tenor' is 't'.
'recital'+'isnt'='recitalisnt'
'recitalisnt' is an anagram of 'clarinettis'.
'clarinettis'+'t'='CLARINETTIST'
(Other definitions for clarinettist that I've seen before include "Cats in litter (anag) -- woodwind player" , "Musician, like Benny Goodman, say" .)