Play boisterously (4)
I believe the answer is:
romp
'play boisterously' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for romp that I've seen before include "Make merry at prom" , "Light-hearted film; easy victory" , "Easy victory; play around energetically" , "light-hearted outing" , "Rough play; easy victory" .)