Maintain there's some body in the beer (6)
I believe the answer is:
allege
'maintain' is the definition.
(I know that allege is a more specific form of the action maintain)
'some body in the beer' is the wordplay.
'some body' becomes 'leg' (I can't justify this - if you can you should give a lot more credence to this answer).
'in the' indicates putting letters inside.
'beer' becomes 'ale' (type of beer).
'leg' placed into 'ale' is 'ALLEGE'.
'there's' acts as a link.
Can you help me to learn more?
(Other definitions for allege that I've seen before include "hold" , "Accuse without established proof" , "Aver - maintain" , "Make a claim without proof" , "State as a fact without proof" .)