Speeds upset US opera, initially proving inappropriate (5)
I believe the answer is:
tempi
'speeds' is the definition.
(I've seen this in another clue)
'upset us opera initially proving inappropriate' is the wordplay.
'upset us opera' becomes 'tem' (I can't justify this - if you can you should give a lot more credence to this answer).
'initially' suggests taking the first letters.
The first letters of 'proving inappropriate' is 'pi'.
'tem'+'pi'='TEMPI'
Can you help me to learn more?
(Other definitions for tempi that I've seen before include "Speeds (music)" , "Speeds for musicians" , "Times" , "Speed controls" , "Speeds, rhythms of musical pieces" .)