Hard to crack clues say rewritten for tragic author (9)
I believe the answer is:
aeschylus
'tragic author' is the definition.
(ancient author of tragedies)
'hard to crack clues say rewritten' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'to crack' is an insertion indicator (inserted letters crack into others).
'rewritten' indicates an anagram.
'clues'+'say'='cluessay'
'cluessay' anagrammed gives 'aescylus'.
'h' inserted inside 'aescylus' is 'AESCHYLUS'.
'for' acts as a link.
(Other definitions for aeschylus that I've seen before include "Greek tragedian (Oresteia)" , "Old stager" , "classical author" , "Ancient Greek dramatist (Oresteia trilogy)" , "Classical Greek playwright" .)