Unexpected resistance crushed by leader of Spanish revolution (10)
I believe the answer is:
surprising
'unexpected' is the definition.
('surprising' is associated in meaning with 'unexpected')
'resistance crushed by leader of spanish revolution' is the wordplay.
'resistance' becomes 'r' (abbreviation).
'crushed by' indicates putting letters inside.
'leader of' says to take the initial letters.
'revolution' becomes 'uprising' (I've seen this before**).
The initial letter of 'spanish' is 's'.
's'+'uprising'='suprising'
'r' going within 'suprising' is 'SURPRISING'.
(Other definitions for surprising that I've seen before include "Causing astonishment" , "Unexpected" , "Mildly astonishing" .)