Agency arresting scoundrel, a chirpy type (6)
I believe the answer is:
cicada
'a chirpy type' is the definition.
(I've seen this before)
'agency arresting scoundrel' is the wordplay.
'agency' becomes 'CIA' (CIA is an example).
'arresting' is an insertion indicator.
'scoundrel' becomes 'cad' (cad is a kind of scoundrel).
'cia' going around 'cad' is 'CICADA'.
(Other definitions for cicada that I've seen before include "Chirpy little thing" , "Bug sounding at night" , "Noisy bug" , "Shrill insect" , "Large bug" .)