Writer having answer to sit back (5)
I believe the answer is:
aesop
'writer' is the definition.
(I've seen this before)
'answer to sit back' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'to sit' becomes 'pose' ('pose' can be a synonym of 'sit').
'back' is a reversal indicator.
'pose' backwards is 'esop'.
'a'+'esop'='AESOP'
'having' is the link.
(Other definitions for aesop that I've seen before include "Ancient Greek author of moral tales" , "Fabulous writer" , "Greek father of fables" , "satirical writer" , "very old writer" .)