Inflexible soldier breaking free (5)
I believe the answer is:
rigid
'inflexible' is the definition.
('rigid' can be a synonym of 'inflexible')
'soldier breaking free' is the wordplay.
'soldier' becomes 'gi' (government issue or general issue).
'breaking' means one lot of letters goes inside another.
'free' becomes 'rid' ('rid' can be a synonym of 'free').
'gi' placed into 'rid' is 'RIGID'.
(Other definitions for rigid that I've seen before include "Firmly fixed" , "Stiff, unyielding" , "Frozen" , "Stiff and inflexible" , "Uncompromising" .)