Crackpot, going back, is getting capital in Africa (5)
I believe the answer is:
tunis
'capital in africa' is the definition.
(capital of Tunisia)
'crackpot going back is getting' is the wordplay.
'crackpot' becomes 'nut' (synonyms).
'going back' is a reversal indicator.
'getting' is a charade indicator (letters next to each other).
'nut' backwards is 'tun'.
'tun'+'is'='TUNIS'
(Other definitions for tunis that I've seen before include "Capital of a republic in north Africa" , "Tom, Dick or Harry" , "North African location" , "I stun (anag) - port and capital" , "N African port" .)