Ben is out to be a writer (5)
I believe the answer is:
ibsen
'a writer' is the definition.
(dramatist Henrik Ibsen)
'ben is out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'ben'+'is'='benis'
'benis' with letters rearranged gives 'IBSEN'.
'to be' acts as a link.
(Other definitions for ibsen that I've seen before include "Norwegian playwright, d. 1906" , "Norwegian author of 'Peer Gynt' etc" , "Norwegian playwright (Peer Gynt)" , "Norwegian dramatist, d. 1906" , "See 7 Down" .)