Stupidly leaving it for unofficial policeman (9)
I believe the answer is:
vigilante
'unofficial policeman' is the definition.
(I've seen this before)
'stupidly leaving it' is the wordplay.
'stupidly' is an anagram indicator.
'leaving'+'it'='leavingit'
'leavingit' is an anagram of 'VIGILANTE'.
'for' acts as a link.
(Other definitions for vigilante that I've seen before include "Policeman unofficially" , "Self-appointed upholder of the law" , "Unofficial security figure" , "Man on patrol" , "Sort of PC not formally recognised" .)