One playing the piano in support? (5)
I believe the answer is:
piper
'one playing' is the definition.
(I've seen this before)
'piano in support?' is the wordplay.
'piano' becomes 'p' (musical abbreviation).
'in' indicates putting letters inside.
'support?' becomes 'pier' (type of structure).
'p' going inside 'pier' is 'PIPER'.
'the' is the link.
(Other definitions for piper that I've seen before include "'Liam O'Flynn or Seamus Ennis, say (5)'" , "If you pay him, call the tune" , "Wind instrumentalist" , "Musician (paid for a tune?)" , "Highland musician" .)