Knock back beer, some amount, in style (4)
I believe the answer is:
elan
'style' is the definition.
(I know that dash can be written as elan)
'knock back beer some amount' is the wordplay.
'knock back' is a reversal indicator.
'beer' becomes 'ale' (type of beer).
'some amount' becomes 'n' (in maths, n can represent any number).
'ale' backwards is 'ela'.
'ela'+'n'='ELAN'
'in' acts as a link.
(Other definitions for elan that I've seen before include "Panache - ardour" , "Dash in France" , "Vitality" , "Snap" , "French verve" .)