Band with zero sex appeal upset arrangement (13)
I believe the answer is:
orchestration
'upset arrangement' is the definition.
'orchestration' can be an answer for 'arrangement' (orchestration is a kind of arrangement). I'm not sure about the 'upset' bit.
'band with zero sex appeal' is the wordplay.
'band' becomes 'orchestra' (I've seen this before).
'with zero sex appeal' becomes 'tion' (I am not sure about this - if you are sure you should believe this answer much more).
'orchestra'+'tion'='ORCHESTRATION'
Can you help me to learn more?
(Other definitions for orchestration that I've seen before include "Scoring for strings, brass, woodwind and percussion" , "Arrangement of string, brass, woodwind and percussion parts" , "Stage-management" , "Arrangement for instruments - short reaction (anag)" , "Composer's skill" .)