Specialised in turning revolutionary (5)
I believe the answer is:
niche
'specialised' is the definition.
(I've seen this in another clue)
'in turning revolutionary' is the wordplay.
'turning' shows that the letters should be reversed in order.
'revolutionary' becomes 'che' (Che Guevara the Marxist revolutionary).
'in' reversed gives 'ni'.
'ni'+'che'='NICHE'
(Other definitions for niche that I've seen before include "Calling" , "Suitable position (in market, life etc)" , "Comfortable position" , "somewhere comfortable" , "Shallow recess in a wall" .)