Revolutionary astrologer offers to provide sacrifice (6)
I believe the answer is:
forego
'sacrifice' is the definition.
'revolutionary astrologer offers to provide' is the wordplay.
'revolutionary' says the letters should be written in reverse.
'provide' indicates the answer is hidden within the clue.
'ogerof' can be found hidden inside 'astrologer offers to'.
'ogerof' back-to-front is 'FOREGO'.
(Other definitions for forego that I've seen before include "Precede (in place/time)" , "Go without or precede" , "Relinquish - do without" , "Go without (something desirable)" , "Surrender" .)