Subordinate part in inferior play (6,6)
I believe the answer is:
second fiddle
'subordinate part' is the definition.
(playing second fiddle means having a minor role)
'inferior play' is the wordplay.
'inferior' becomes 'second' (inferior can mean secondary or less important).
'play' becomes 'fiddle' (fiddling is a kind of playing).
'second'+'fiddle'='SECOND FIDDLE'
'in' acts as a link.
(Other definitions for second fiddle that I've seen before include "not of the first rank" , "Subordinate role" , "should take a bow?" , "Junior player" , "Dry" .)