Chasing some secret fantasies in retirement (5)
I believe the answer is:
after
'chasing' is the definition.
(I've seen this before)
'secret fantasies in retirement' is the wordplay.
'in' says the answer is hidden in the clue.
'retirement' is a reversal indicator (retire can mean to return or go back).
'retfa' is hidden in the letters of 'secret fantasies'.
'retfa' written backwards gives 'AFTER'.
'some' acts as a link.
(Other definitions for after that I've seen before include "In pursuit of, behind" , "In honour of" , "Post, later than" , "At a later time or behind" , "Following - behind" .)