Besides being about to err badly as a bullfighter (6)
I believe the answer is:
torero
'a bullfighter' is the definition.
('torero' can be a synonym of 'bullfighter')
'besides being about to err badly' is the wordplay.
'besides' becomes 'too' (both can mean 'in addition').
'being about' means one lot of letters goes inside another.
'badly' is an anagram indicator.
'err' with letters rearranged gives 'rer'.
'too' going around 'rer' is 'TORERO'.
'as' acts as a link.
(Other definitions for torero that I've seen before include "hero in the ring" , "Bullfighter" , "Escamillo, for example" , "Spanish fighter" , "Bullring occupant" .)