FBI agents placed outside division (7)
I believe the answer is:
segment
'division' is the definition.
(I've seen this before)
'fbi agents placed outside' is the wordplay.
'fbi agents' becomes 'gmen' ('G-man' can be a synonym of 'fbi agent').
'placed' becomes 'set' (synonyms).
'outside' means one lot of letters goes inside another.
'gmen' placed within 'set' is 'SEGMENT'.
(Other definitions for segment that I've seen before include "Part separable from other parts, say of orange" , "One of several parts of a whole" , "Part of citrus fruit" , "Division" , "Part of a circle cut off by a chord" .)