Ballroom activity (7)
I believe the answer is:
dancing
'ballroom activity' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for dancing that I've seen before include "Moving to music" , "Taking a series of rhythmical steps and movements in time to music" , "Terpsichorean exercise" , "Performing ballet" , "Strictly Come - - (TV)" .)