Claim supporter is into the beer (6)
I believe the answer is:
allege
'claim' is the definition.
(I've seen this in another clue)
'supporter is into the beer' is the wordplay.
'supporter' becomes 'leg' (I've seen this in another clue).
'is into' is an insertion indicator.
'the beer' becomes 'ale' (type of beer).
'leg' put within 'ale' is 'ALLEGE'.
(Other definitions for allege that I've seen before include "Declare without actual proof" , "Claim (a person is guilty)" , "Swear" , "Declare or assert without proof" , "Declare without being able to prove" .)