Musician's support includes piano (5)
I believe the answer is:
'musician's' is the definition.
(piper is a kind of musician)
'support includes piano' is the wordplay.
'support' becomes 'pier' (pier is a kind of support).
'includes' is an insertion indicator.
'piano' becomes 'p'.
'pier' placed around 'p' is 'PIPER'.
(Other definitions for piper that I've seen before include "One playing wind instrument" , "Highland instrumentalist" , "Musician (who gets paid?)" , "Military musician" , "John --, 20th century English artist" .)