Blazer to change into for nine? (7)
I believe the answer is:
inferno
'blazer' is the definition.
(something which 'blazes')
'to change into for nine?' is the wordplay.
'to change into' indicates anagramming the letters.
'for'+'nine'='fornine'
'fornine' anagrammed gives 'INFERNO'.
(Other definitions for inferno that I've seen before include "A raging fire as in hell - ask Dante" , "Nine Circles here" , "Large dangerous fire" , "Furious" , "Fierce fire" .)