Claim it's a legal fiddle at closing time (6)
I believe the answer is:
allege
'claim' is the definition.
(to allege something is to make a claim)
'a legal fiddle at closing time' is the wordplay.
'fiddle' indicates anagramming the letters.
'at' means one lot of letters go next to another.
'closing time' becomes 'e' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'legal' is an anagram of 'alleg'.
'alleg'+'e'='ALLEGE'
'it's' is the link.
Can you help me to learn more?
(Other definitions for allege that I've seen before include "Claim, suggest" , "Accuse without established proof" , "Assert, state without proof" , "Declare or accuse without proof" , "Cite in discussion" .)