Street cop being beaten up is confidential (3,6)
I believe the answer is:
top secret
'confidential' is the definition.
(I've seen this before)
'street cop being beaten up' is the wordplay.
'being beaten up' is an anagram indicator.
'street'+'cop'='streetcop'
'streetcop' is an anagram of 'TOP-SECRET'.
'is' acts as a link.
(Other definitions for top secret that I've seen before include "restricted" , "Of the highest security classification" , "As 007 mission" , "the knack of sleeping well?" , "(Of information) strictly not for public consumption" .)