Act of revolution (4)
I believe the answer is:
turn
I believe this clue is a double definition.
'act' is the first definition.
(theatre)
'revolution?' is the second definition.
(revolution can mean a turn or rotation)
'of' is the link.
(Other definitions for turn that I've seen before include "Distinctive expression" , "Revolve - go off" , "See 19" , "Go; spin (cricket)" , "rotation" .)