Go over a fault (6)
I believe the answer is:
defect
I believe this is a double definition.
'go over' is the first definition.
(to defect is to go over to the other side)
'a fault' is the second definition.
('defect' can be a synonym of 'fault')
(Other definitions for defect that I've seen before include "Desert - fault" , "Transfer allegiance to opposition" , "Fault, flaw" , "Fault - default" , "Deficiency" .)