Quiet craftsman, biased (8)
I believe the answer is:
partisan
'biased' is the definition.
(I've seen this before)
'quiet craftsman' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano').
'craftsman' becomes 'artisan' ('artisan' can be a synonym of 'craftsman').
'p'+'artisan'='PARTISAN'
(Other definitions for partisan that I've seen before include "champion" , "Devotee of a cause" , "type of spear" , "Enthusiastic supporter" , "Adherent" .)