Work or play using symphonic leaders (4)
I believe the answer is:
opus
'work' is the definition.
(an opus is an artistic work)
'or play using symphonic leaders' is the wordplay.
'leaders' indicates taking the first letters.
The first letters of 'or play using symphonic' is 'OPUS'.
(Other definitions for opus that I've seen before include "Creative work, eg in writing, art or music" , "A Latin work" , "Work (mus.)" , "Work of 25 perhaps" , "Musical piece" .)