Follow up about a source of rope — this rope? (6)
I believe the answer is:
lariat
'this rope?' is the definition.
(lariat is a kind of rope)
'follow up about a source of rope' is the wordplay.
'follow' becomes 'tail' (I've seen this before).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'about' indicates putting letters inside.
'source of' says to take the initial letters.
The first letter of 'rope' is 'r'.
'tail' reversed gives 'liat'.
'a'+'r'='ar'
'liat' going around 'ar' is 'LARIAT'.
(Other definitions for lariat that I've seen before include "Rope for the cowboy" , "Cowcatcher" , "Tethering rope" , "Mortar-spreading tool" , "Long rope with a noose at the end" .)