Confidential street cop deployed (3-6)
I believe the answer is:
top-secret
'confidential' is the definition.
(I've seen this before)
'street cop deployed' is the wordplay.
'deployed' indicates an anagram.
'street'+'cop'='streetcop'
'streetcop' with letters rearranged gives 'TOP-SECRET'.
(Other definitions for top-secret that I've seen before include "Highly classified" , "Extremely restricted (information)" , "Highly confidential" , "Of the highest security classification" , "Very hush-hush" .)