A fool going back in, disinterested (5)
I believe the answer is:
aloof
'disinterested' is the definition.
(I've seen this before)
'a fool going back' is the wordplay.
'going back' is a reversal indicator.
'fool' back-to-front is 'loof'.
'a'+'loof'='ALOOF'
'in' is the link.
(Other definitions for aloof that I've seen before include "Haughty and distant like a fool" , "Distant in manner" , "Indifferent - by oneself" , "Unpleasantly cold" , "Distant or stuck-up" .)