Players roar frantically defending box (9)
I believe the answer is:
orchestra
'players' is the definition.
(group playing music)
'roar frantically defending box' is the wordplay.
'frantically' indicates anagramming the letters.
'defending' indicates putting letters inside (inserted letters are defended).
'box' becomes 'chest' (chest is a kind of box).
'roar' with letters rearranged gives 'orra'.
'orra' going around 'chest' is 'ORCHESTRA'.
(Other definitions for orchestra that I've seen before include "Brass, woodwind, strings and percussion" , "Large body of musicians" , "Large band of players" , "players in pit" , "Other cars (anag.)" .)