Government, say, blocking revolutionary ruler (6)
I believe the answer is:
regime
'government' is the definition.
(I know that government can be written as regime)
'say blocking revolutionary ruler' is the wordplay.
'say' becomes 'eg' (both can mean 'for example').
'blocking' means one lot of letters goes inside another (block can mean to plug a gap in something).
'revolutionary' says the letters should be written backwards (letters revolve around).
'ruler' becomes 'emir' (historical term for a Muslim ruler).
'emir' in reverse letter order is 'rime'.
'eg' inserted into 'rime' is 'REGIME'.
(Other definitions for regime that I've seen before include "The government in power or systematic plan" , "A governing administration" , "Command" , "co-ordinated programme" , "Emigre (anag.)" .)