Banish revolutionary understood to be engaged in subterfuge (9)
I believe the answer is:
rusticate
'banish' is the definition.
(rusticating is a kind of banishing)
'revolutionary understood to be engaged in subterfuge' is the wordplay.
'revolutionary' is a reversal indicator.
'understood' becomes 'tacit' (I've seen this before**).
'to be engaged in' is an insertion indicator.
'subterfuge' becomes 'ruse' (I've seen this before).
'tacit' back-to-front is 'ticat'.
'ticat' inserted into 'ruse' is 'RUSTICATE'.
(Other definitions for rusticate that I've seen before include "Ban from college" , "Send away" , "Suspend from university" , "send down student" , "leave town" .)