Police officer's outstanding aim, tackling place of iniquity (14)
I believe the answer is:
superintendent
'police officer's' is the definition.
(superintendent is a rank of police officer)
'outstanding aim tackling place of iniquity' is the wordplay.
'outstanding' becomes 'super' (super can mean very good).
'aim' becomes 'intent' (synonyms).
'tackling' is an insertion indicator (to tackle is to take possession of).
'place of iniquity' becomes 'den' (I've seen this in another clue).
'intent' placed around 'den' is 'intendent'.
'super'+'intendent'='SUPERINTENDENT'
(Other definitions for superintendent that I've seen before include "One who is in charge of an organisation" , "Police rank" , "Overseer; police officer" , "Senior police officer" , "Police chief" .)