Suppose the old revolt? (8)
I believe the answer is:
theorise
'suppose' is the definition.
('theorise' can be a synonym of 'suppose')
'the old revolt?' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'revolt?' becomes 'rise' (revolting is a kind of rising).
'the'+'o'+'rise'='THEORISE'
(Other definitions for theorise that I've seen before include "Think up possible explanations" , "Form view" , "Conjecture, hypothesise" , "Express ideas" , "Form of hypothesis or conjecture" .)