All-out event is in disarray (9)
I believe the answer is:
intensive
'all-out' is the definition.
(thesaurus)
'event is in disarray' is the wordplay.
'disarray' indicates anagramming the letters.
'event'+'is'+'in'='eventisin'
'eventisin' with letters rearranged gives 'INTENSIVE'.
(Other definitions for intensive that I've seen before include "Very vigorous or thorough; concentrating" , "Demanding" , "Concentrated" .)