Over 100 casinos prepared for events (9)
I believe the answer is:
occasions
'events' is the definition.
(occasion is a kind of event)
'over 100 casinos prepared' is the wordplay.
'over' becomes 'o' (cricket abbreviation).
'o00' becomes 'C' (Roman numeral).
'prepared' is an anagram indicator.
'casinos' anagrammed gives 'casions'.
'o'+'c'+'casions'='OCCASIONS'
'for' acts as a link.
(Other definitions for occasions that I've seen before include "Causes to happen" , "Special times or events" , "Social events" , "Celebrations" .)