Under fire, however, players blew it (7)
I believe the answer is:
sackbut
'players blew it' is the definition.
(historical type of trombone)
'under fire however' is the wordplay.
'under' is a charade indicator (letters next to each other).
'fire' becomes 'sack' (dismiss someone from their job).
'however' becomes 'but' (I've seen this before).
'sack'+'but' is 'SACKBUT'.
(Other definitions for sackbut that I've seen before include "Old trombone" , "music maker" , "Medieval form of trombone" , "Ancient musical instrument" , "music-maker" .)