Nat has returned to South Africa with a bit of poetry (6)
I believe the answer is:
stanza
'bit of poetry' is the definition.
'nat has returned to south africa with a' is the wordplay.
'nat has' becomes 'ts' (I am not sure about this - if you are sure you should believe this answer much more).
'returned' says the letters should be written backwards.
'to south africa' becomes 'za' (abbreviation for Zuid-Afrika).
'with' means one lot of letters go next to another.
'a' becomes 'an'.
'ts' in reverse letter order is 'st'.
'za' put after 'an' is 'anza'.
'st'+'anza'='STANZA'
(Other definitions for stanza that I've seen before include "piece by poet" , "Lines forming a unit of verse" , "Lines of poetry forming a pattern" , "Part of a poem" , "Group of poetic lines" .)