Claim limb is dipped in beer (6)
I believe the answer is:
'claim' is the definition.
(I've seen this before)
'limb is dipped in beer' is the wordplay.
'limb' becomes 'leg' (leg is a kind of limb).
'is dipped in' means one lot of letters goes inside another.
'beer' becomes 'ale' (type of beer).
'leg' going within 'ale' is 'ALLEGE'.
(Other definitions for allege that I've seen before include "Swear" , "Aver - maintain" , "Declare without absolute proof" , "Make accusation without proof" , "Declare or assert without proof" .)