Rise up (5)
I believe the answer is:
rebel
'rise up' is the definition.
(I know that rise up can be written as rebel)
This is the entire clue.
(Other definitions for rebel that I've seen before include "One who opposes the powerful" , "(One who) revolt(s)" , "Rise up (without a cause?)" , "One refusing to conform" , "Bolshy" .)