Player with so boisterous a part (6)
I believe the answer is:
oboist
'player' is the definition.
(oboe player)
'with so boisterous a part' is the wordplay.
'with' indicates the answer is hidden within the clue.
'OBOIST' can be found hidden inside 'so boisterous part'.
(Other definitions for oboist that I've seen before include "Musician who plays woodwind of treble pitch" , "Instrumentalist" , "orchestra member" , "Do I boost the musician?" , "Player of woodwind instrument of treble pitch" .)