Knotty problem unravelling ropes (5)
I believe the answer is:
poser
'knotty problem' is the definition.
(I've seen this in another clue)
'unravelling ropes' is the wordplay.
'unravelling' is an anagram indicator.
'ropes' is an anagram of 'POSER'.
(Other definitions for poser that I've seen before include "Toughie" , "Puzzling question for the model" , "Particularly baffling problem" , "Tricky problem" , "Exhibitionist" .)