Girl played a banjo topless? Not initially (6)
I believe the answer is:
joanna
'girl' is the definition.
'played a banjo topless? not initially' is the wordplay.
'played' indicates anagramming the letters (letters playing around).
'topless?' means to remove the first letter (I've seen 'topless' mean this).
'initially' indicates taking the first letters.
The initial letter of 'not' is 'n'.
'banjo' with its initial letter removed is 'anjo'.
'a'+'anjo'+'n'='aanjon'
'aanjon' is an anagram of 'JOANNA'.
(Other definitions for joanna that I've seen before include "Girl's name, piano" , "east end piano" , "Piano (rhyming slang)" , "One's played" .)