Ball can be made square (10)
I believe the answer is:
masquerade
'ball' is the definition.
(masquerade ball is a kind of ball)
'can be made square' is the wordplay.
'can' indicates anagramming the letters (I've seen 'canned' mean this (canned can mean drunk)).
'made'+'square'='madesquare'
'madesquare' anagrammed gives 'MASQUERADE'.
(Other definitions for masquerade that I've seen before include "where everyone's wearing the veil" , "Pretence - masked ball" , "Costume party" , "Dress up" , "pose" .)