Brawls occasionally seen before line dance (4)
I believe the answer is:
ball
'dance' is the definition.
(ball is a kind of dance)
'brawls occasionally seen before line' is the wordplay.
'occasionally' indicates alternate letters.
'seen before' says to put letters next to each other.
'line' becomes 'l' (used when specifying particular lines from a poem).
The alternating letters of 'brawls' are 'bal'.
'bal'+'l'='BALL'
(Other definitions for ball that I've seen before include "Spherical object" , "Squash, say" , "All-round" , "20" , "Party" .)