Bar's last pot to clear up (9)
I believe the answer is:
blackball
'clear up' is the definition.
Although both the answer and definition are verbs in their base form, I can't understand how they can define each other.
'bar's last pot' is the wordplay.
'bar' becomes 'black' (to black certain goods is to boycott them).
'last pot' becomes 'ball' (I can't explain this - if you can you should believe this answer much more).
'black'+'ball'='BLACKBALL'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for blackball that I've seen before include "Ostracise" , "bar?" , "Veto (membership)" , "Exclude by a negative vote" , "Reject" .)