Resists, stands up to (6)
I believe the answer is:
defies
I believe this is a double definition.
'resists' is the first definition.
('defy' can be a synonym of 'resist')
'stands up to' is the second definition.
(I've seen this in another clue)
(Other definitions for defies that I've seen before include "Braves, dares; flouts" , "Openly resists" , "Refuses to comply or obey someone" , "Boldly refuses to obey" , "Refuses to obey, challenges" .)