Where one conducts or turns up to play unskilfully (7)
I believe the answer is:
rostrum
'where one conducts' is the definition.
(a rostrum is a raised stage a conductor might use)
'or turns up to play unskilfully' is the wordplay.
'turns up' shows that the letters should be reversed in order.
'to play unskilfully' becomes 'strum' (eg strumming a guitar).
'or' reversed gives 'ro'.
'ro'+'strum'='ROSTRUM'
(Other definitions for rostrum that I've seen before include "At which one may conduct" , "Platform for orchestra conductor" , "Conductor's dais" , "beak" , "Podium" .)