Note everyone at the dance (4)
I believe the answer is:
'the dance' is the definition.
(ball is a kind of dance)
'note everyone' is the wordplay.
'note' becomes 'b' (musical note).
'everyone' becomes 'all' (all people).
'at' is the link.
(Other definitions for ball that I've seen before include "Formal dance gathering" , "Social function for dancing" , "Formal social event" , "Party" , "Perhaps a bouncer < 's clog" .)