Sure it won’t get muddled? It’s hard to say (6,7)
I believe the answer is:
tongue twister
'it's hard to say' is the definition.
(I've seen this in another clue)
'sure it won't get muddled?' is the wordplay.
'muddled?' indicates anagramming the letters (I've seen 'muddled' mean this).
'sure'+'it'+'wont'+'get'='sureitwontget'
'sureitwontget' is an anagram of 'TONGUE-TWISTER'.
(Other definitions for tongue twister that I've seen before include "Peter Piper picked a peck of pickled pepper, for instance" , "eg 'She sells seashells by the seashore'" , "'I wish to wash my Irish wristwatch', perhaps" , "Sequence of words difficult to say" , "Something hard to pronounce" .)