Possibly sang with difficulty (4)
I believe the answer is:
snag
'difficulty' is the definition.
(I know that snag is a type of obstacle)
'possibly sang' is the wordplay.
'possibly' indicates an anagram.
'sang' anagrammed gives 'SNAG'.
'with' acts as a link.
(Other definitions for snag that I've seen before include "Slight problem" , "Sang about obstacle" , "Catch - disadvantage" , "Minor hitch" , "Hidden obstacle or drawback" .)