Extra work (3,4)
(Other definitions for bit part that I've seen before include "'Small role in film or play (3,4)'" , "Small acting role" , "cameo" , "Tool" , "extra work, perhaps" .)
I believe this clue is a double definition.
'extra' is the first definition.
(extra is a type of cricket run)
'work?' is the second definition.
(both can mean to operate something)
(Other definitions for run that I've seen before include "Possibly an extra" , "Move at speed" , "publish" , "Manage, operate" , "On the . . . - fleeing from pursuit" .)
'extra work' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for overtime that I've seen before include "Hours worked in excess of usual" , "Work beyond normal hours? Remove it" , "Extra hours (at work)" , "Hours worked and paid for beyond the usual amount" , "Work outside normal hours" .)