Leave a Mafia boss outside bar (7)
I believe the answer is:
abandon
'leave' is the definition.
(abandoning is a kind of leaving)
'a mafia boss outside bar' is the wordplay.
'mafia boss' becomes 'don' (I've seen this before).
'outside' is an insertion indicator.
'bar' becomes 'ban' (I've seen this before).
'a'+'don'='adon'
'adon' placed around 'ban' is 'ABANDON'.
(Other definitions for abandon that I've seen before include "Permanently desert" , "Give up (something) completely" , "Kick" , "Desert or yield without restraint" , "Forsake - careless freedom" .)