Mad role played by title (7)
I believe the answer is:
earldom
'title' is the definition.
(title or rank of an earl)
'mad role played' is the wordplay.
'played' indicates an anagram (letters playing around).
'mad'+'role'='madrole'
'madrole' anagrammed gives 'EARLDOM'.
'by' acts as a link.
(Other definitions for earldom that I've seen before include "Units" , "Noble rank" , "Essex?" , "Norfolk or Wessex, for example" , "A noble's lands or title" .)