Bagging 500 in opening spell of bowling is excessive (8)
I believe the answer is:
overdone
'is excessive' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
(Other definitions for overdone that I've seen before include "Exaggerated; cooked too much" , "Cooked too much or carried too far" , "Hammed up" , "Exaggerated - far from rare" , "Exaggerated; burnt (meat)" .)