Wagner's first to abandon important scores (6)
I believe the answer is:
eighty
'scores' is the definition.
(I've seen this before)
'wagner's first to abandon important' is the wordplay.
'wagner's first' becomes 'w' (1st letter of 'wagner').
'to abandon' is a deletion indicator.
'important' becomes 'weighty' (weighty can mean influential or important).
'weighty' with 'w' removed is 'EIGHTY'.
(Other definitions for eighty that I've seen before include "Several score" , "Figure" , "'Nineteen -- Four' (novel)" , "score less than a hundred" , "not many score" .)