Revolutionary incentive after prison support for rider (8)
I believe the answer is:
stirrups
'support for rider' is the definition.
'revolutionary incentive after prison' is the wordplay.
'revolutionary' says the letters should be written in reverse.
'incentive' becomes 'spur' (I've seen this before).
'after' means one lot of letters go next to another.
'prison' becomes 'stir' (informal term for prison**).
'spur' reversed gives 'rups'.
'rups' put after 'stir' is 'STIRRUPS'.
(Other definitions for stirrups that I've seen before include "Riding equipment" , "Riders' foot-rests" , "Horsemen put their feet in them" , "Metal loops for rider's feet" , "Horseman put his feet in them" .)