It's finished after six balls (4)
I believe the answer is:
over
I believe this clue is a double definition.
'it's finished' is the first definition.
(over can mean finished or ended)
'six balls' is the second definition.
(cricket)
'after' acts as a link.
(Other definitions for over that I've seen before include "Finished; six balls" , "Given too much money" , "Finished-up -left" , "Passed" , "Six balls in cricket" .)