Musicians in piano coats (7)
I believe the answer is:
players
'musicians' is the definition.
('player' can be a synonym of 'musician')
'piano coats' is the wordplay.
'piano' becomes 'p' (musical abbreviation).
'coats' becomes 'layers' (layering is a kind of coating).
'p'+'layers'='PLAYERS'
'in' is the link.
(Other definitions for players that I've seen before include "Team members" , "They participate in games" , "Actors" , "cast" , "Musicians" .)