Turn on radio for character in play (4)
I believe the answer is:
role
'character in play' is the definition.
'turn on radio' is the wordplay.
'turn' becomes 'roll' (roll is a kind of turn).
'on radio' indicates a 'sounds like' (homophone) clue.
'roll' is a homophone of 'ROLE'.
'for' is the link.
(Other definitions for role that I've seen before include "Function in life" , "Function; part" , "Acting part" , "Part (in drama)" , "Playing part" .)