Champion to drink stout (9)
I believe the answer is:
supporter
'champion' is the definition.
('supporter' can be a synonym of 'champion')
'drink stout' is the wordplay.
'drink' becomes 'sup' (I've seen this before).
'stout' becomes 'porter' ('porter' can be a synonym of 'stout').
'sup'+'porter'='SUPPORTER'
'to' acts as a link.
(Other definitions for supporter that I've seen before include "Second" , "sports fan?" , "Advocate" , "Stay" , "Strut" .)