Rebellion? Reluctantly at first I reveal all (6)
I believe the answer is:
rising
'rebellion?' is the definition.
('rising' can be a synonym of 'rebellion')
'reluctantly at first i reveal all' is the wordplay.
'at first' suggests taking the first letters.
'reveal all' becomes 'sing' (sing can mean to confess or inform the police).
The initial letter of 'reluctantly' is 'r'.
'r'+'i'+'sing'='RISING'
(Other definitions for rising that I've seen before include "Armed revolt against authority" , "Upwardly mobile" , "Upward rebellion?" , "Mutiny" , "Sloping up; rebellion" .)