He has a line in chaff (5)
I believe the answer is:
brian
'he' is the definition.
'a line in chaff' is the wordplay.
I cannot quite understand how this works, but
'a' could be 'an' and 'an' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'has' acts as a link.
Can you help me to learn more?
(Other definitions for brian that I've seen before include "-- Blessed, actor" , "-- Blessed; -- Eno" , "He had a 1979 film "Life"!" , "snail animated" , "intellect" .)