Author errs -- man ill-suited to be an author (6,7)
I believe the answer is:
arthur ransome
'author' is the definition.
'author errs man ill-suited' is the wordplay.
'ill-suited' indicates anagramming the letters.
'author'+'errs'+'man'='authorerrsman'
'authorerrsman' anagrammed gives 'ARTHUR RANSOME'.
'to be an' is the link.
(Other definitions for arthur ransome that I've seen before include "Children's author" , "Swallows and Amazons author" .)