Dance a long time holding popular dancer (9)
I believe the answer is:
ballerina
'dancer' is the definition.
(ballerina is a kind of dancer)
'dance a long time holding popular' is the wordplay.
'dance' becomes 'ball' (ball is a kind of dance**).
'a long time' becomes 'era' (I've seen this before).
'holding' is an insertion indicator.
'popular' becomes 'in'.
'era' placed around 'in' is 'erina'.
'ball'+'erina'='BALLERINA'
(Other definitions for ballerina that I've seen before include "Dancers" , "girl on point duty" , "Female dancer, could be prima" , "Female classical dancer" , "lass good at splits?" .)