Song and dance over commercial (6)
I believe the answer is:
ballad
'song' is the definition.
(I know that ballad is a type of song)
'dance over commercial' is the wordplay.
'dance' becomes 'ball' (ball is a kind of dance).
'over' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'commercial' becomes 'ad' (abbreviation for advertisement).
'ball'+'ad'='BALLAD'
'and' acts as a link.
(Other definitions for ballad that I've seen before include "Narrative song with a recurrent refrain" , "Simple song or poem" , "romance" , "A simple or old song" , "Narrative poem or song" .)