Struggle to eat a bone (6)
I believe the answer is:
sacrum
'bone' is the definition.
(sacrum is a kind of bone)
'struggle to eat a' is the wordplay.
'struggle' becomes 'scrum' (I have seen 'Disorderly struggle ' mean 'scrum' so perhaps 'struggle' could also mean 'scrum').
'to eat' indicates putting letters inside.
'scrum' enclosing 'a' is 'SACRUM'.
(Other definitions for sacrum that I've seen before include "Bone in the lower back" , "Triangular bone that forms back of pelvis" , "Triangular bone forming back of pelvis" , "Wedge-shaped bone forming the back part of the pelvis" .)