Insubordination in Spain's greatly outside the box (6)
I believe the answer is:
mutiny
'insubordination' is the definition.
(thesaurus)
'spain's greatly outside the box' is the wordplay.
'spain's greatly' becomes 'muy' ('very' or 'greatly' in Spanish).
'outside' indicates putting letters inside.
'the box' becomes 'tin' (I can't explain this - if you can you should give a lot more credence to this answer).
'muy' going around 'tin' is 'MUTINY'.
'in' acts as a link.
(Other definitions for mutiny that I've seen before include "Military rebellion" , "Revolt against authority" , "Rebellion as on Bligh's Bounty" , "Rebellion in the armed forces" , "Insurrection" .)