Contents of lager after American tradition (5)
I believe the answer is:
usage
'tradition' is the definition.
(I've seen this before)
'contents of lager after american' is the wordplay.
'contents of' means to look at the middle letters (the letters on the inside of the word).
'after' means one lot of letters go next to another.
'american' becomes 'US' (abbreviation for United States).
The middle letters of 'lager' are 'age'.
'age' put after 'us' is 'USAGE'.
(Other definitions for usage that I've seen before include "Usual practice" , "Way of treating" , "Silly little thing" , "Customary way in which language is spoken or written" , "Custom - treatment" .)