Actor in a run (5)
I believe the answer is:
extra
I believe this is a double definition.
'actor' is the first definition.
(extra is a kind of actor)
'a run' is the second definition.
(cricket run)
'in' acts as a link.
(Other definitions for extra that I've seen before include "Something additional or bit player in movie" , "someone in a crowd scene" , "Crowd-scene actor" , "Left over" , "No-ball or wide, perhaps?" .)