When it's broken, that's good (3)
I believe the answer is:
par
'when it's broken that's good' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for par that I've seen before include "Average standard" , "State of equality" , "Average or normal score" , "Average or even, as for the course" , "Average - equality" .)