Deny scarfs used for certain ball wear (5,5)
I believe the answer is:
fancy dress
'certain ball wear' is the definition.
'fancy dress' can be an answer for 'wear' (fancy dress is a kind of wear). I am not sure about the 'certain ball' bit.
'deny scarfs used' is the wordplay.
'used' indicates an anagram.
'deny'+'scarfs'='denyscarfs'
'denyscarfs' is an anagram of 'FANCY DRESS'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for fancy dress that I've seen before include "Party costume" , "Masquerade costume?" , "Frivolous party garb" , "Themed party attire" .)