Host a Chelsea ball? (9)
I believe the answer is:
abundance
'host' is the definition.
(I've seen this before)
'a chelsea ball?' is the wordplay.
'chelsea' becomes 'bun' (Chelsea bun is an example).
'ball?' becomes 'dance' (ball is a kind of dance).
'a'+'bun'+'dance'='ABUNDANCE'
(Other definitions for abundance that I've seen before include "Nine tricks" , "Host" , "Plenty, profusion" , "great deal" , "Heaps of" .)