Player who's a bit too boisterous? (6)
I believe the answer is:
oboist
'player' is the definition.
(oboe player)
'a bit too boisterous?' is the wordplay.
'a bit' indicates the answer is hidden within the clue (I've seen 'bit of' mean this).
'OBOIST' is hidden within 'too boisterous'.
'who's' is the link.
(Other definitions for oboist that I've seen before include "orchestra member" , "Instrumentalist" , "Do I boost the musician?" , "Player of woodwind instrument of treble pitch" , "Musician who plays woodwind of treble pitch" .)