Head barman in bar produces a measure synonymous with the journalists (6)
I believe the answer is:
linage
'a measure synonymous with the journalists' is the definition.
I can't judge whether this defines the answer.
'head barman in bar' is the wordplay.
'head barman' becomes 'ag' (I can't explain this - if you can you should believe this answer much more).
'in' indicates putting letters inside.
'bar' becomes 'line' (I've seen this in other clues).
'ag' put within 'line' is 'LINAGE'.
'produces' 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" , "Measure of text length" , "Length of printed piece" , "length of article?" .)