Be outstanding, putting away litres and pint in bar (6)
I believe the answer is:
except
'in bar' is the definition.
(I've seen this before)
'be outstanding putting away litres and pint' is the wordplay.
'be outstanding' becomes 'excel' (someone who excels is outstanding).
'putting away' indicates named letters should be taken away.
'litres' becomes 'L' (abbreviation).
'and' is a charade indicator (letters next to each other).
'pint' becomes 'pt' (abbreviation).
'excel' with 'l' taken out is 'exce'.
'exce'+'pt'='EXCEPT'
(Other definitions for except that I've seen before include "Leave out, exclude" , "Not including, omit this" , "Apart from, excluding" , "Save for" , "Rule out - unless" .)