Fleet’s spell on island hurt girl (7,6)
I believe the answer is:
spanish armada
'fleet's' is the definition.
(16th-century fleet)
'spell on island hurt girl' is the wordplay.
'spell' becomes 'span' (span of time).
'on' is a charade indicator (letters next to each other).
'island' becomes 'i' (geographical abbreviation).
'hurt' becomes 'sharm' (I can't explain this - if you can you should believe this answer much more).
'girl' becomes 'Ada' (girl's name).
'span'+'i'+'sharm'+'ada'='SPANISH ARMADA'
(Other definitions for spanish armada that I've seen before include "Famous naval fleet" , "1588 invasion fleet" , "1588 invasion force" , "Fleet sent against England in 1588" , "Fleet that sailed from Lisbon in May fifteen eighty eight" .)