Frank has to ring a writer (4)
I believe the answer is:
open
'frank' is the definition.
('open' can be a synonym of 'frank')
'to ring a writer' is the wordplay.
'to ring' becomes 'o'.
'a writer' becomes 'pen' (I've seen this before).
'o'+'pen'='OPEN'
'has' is the link.
(Other definitions for open that I've seen before include "Contest that includes all comers" , "Exposed; free" , "Not closed or obstructed" , "Sports contest" , "unsealed" .)