A transition, perhaps, when in charge (5)
I believe the answer is:
segue
'a transition' is the definition.
(eg transition from one scene to another in a film)
'perhaps when in charge' is the wordplay.
'perhaps' becomes 'eg' (for example).
'when in' means one lot of letters goes inside another.
'charge' becomes 'sue' (as in suing somebody in court).
'eg' put inside 'sue' is 'SEGUE'.
(Other definitions for segue that I've seen before include "Move seamlessly from one section to another" , "Go on without interruption" , "Smooth musical transition" , "carry on" , "Follow smoothly on" .)