Cutting back on beer in bar (7)
I believe the answer is:
excerpt
'cutting' is the definition.
(I've seen this before)
'back on beer in bar' is the wordplay.
'back on' indicates one should take the final letters (the letter at the back).
'in' is an insertion indicator.
'bar' becomes 'except' (both can mean 'not including').
The final letter of 'beer' is 'r'.
'r' put inside 'except' is 'EXCERPT'.
(Other definitions for excerpt that I've seen before include "1D [CLIP]" , "newspaper clipping" , "Passage selected from a book" , "Sample of work" , "scrap?" .)