Rating adjusting sail behind a very quiet artist (9)
I believe the answer is:
appraisal
'rating' is the definition.
(I've seen this before)
'adjusting sail behind a very quiet artist' is the wordplay.
'adjusting' indicates anagramming the letters.
'behind' is a charade indicator (letters next to each other).
'very quiet' becomes 'pp' (musical abbreviation for pianissimo).
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'sail' is an anagram of 'isal'.
'a'+'pp'+'ra'='appra'
'isal' put after 'appra' is 'APPRAISAL'.
(Other definitions for appraisal that I've seen before include "Formal assessment of an employee's performance" , "Evaluation - price survey" , "judgment" , "valuation" , "rating" .)