A measure of the newspaperman produced by head barman in bar (6)
I believe the answer is:
linage
'a measure of the newspaperman produced' is the definition.
I can't tell whether this definition defines the answer.
'head barman in bar' is the wordplay.
'head barman' becomes 'ag' (I am not sure about this - if you are sure you should believe this answer much more).
'in' is an insertion indicator.
'bar' becomes 'line' (I've seen this in other clues).
'ag' put inside 'line' is 'LINAGE'.
'by' acts as a link.
Can you help me to learn more?
(Other definitions for linage that I've seen before include "amount of editorial matter" , "Length of printed piece" , "Measure of text length" , "length of article?" .)