Bones are cut in meat: it's proving tricky (9)
I believe the answer is:
metatarsi
'bones' is the definition.
(I've seen this before)
'are cut in meat it's proving tricky' is the wordplay.
'cut' means to remove the last letter.
'in' means one lot of letters goes inside another.
'proving tricky' indicates anagramming the letters (a tricky or confusing ordering of the letters).
'are' with its final letter taken off is 'ar'.
'meat'+'its'='meatits'
'meatits' anagrammed gives 'metatsi'.
'ar' going within 'metatsi' is 'METATARSI'.
(Other definitions for metatarsi that I've seen before include "bones" , "Parts of the feet" .)