One who plays so boisterous a part (6)
I believe the answer is:
oboist
'one who' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'plays so boisterous a part' is the wordplay.
'a part' indicates the answer is hidden within the clue.
'OBOIST' can be found hidden inside 'plays so boisterous'.
Can you help me to learn more?
(Other definitions for oboist that I've seen before include "Instrumentalist" , "orchestra member" , "Do I boost the musician?" , "Wind player" , "Player of woodwind instrument of treble pitch" .)