Winners the night before occupying high chairs (9)
I believe the answer is:
achievers
'winners' is the definition.
('achiever' can be a synonym of 'winner')
'the night before occupying high chairs' is the wordplay.
'the night before' becomes 'eve' (I've seen this before).
'occupying' means one lot of letters goes inside another.
'high' is an anagram indicator (can mean drunk or on drugs and hence disordered).
'chairs' with letters rearranged gives 'achirs'.
'eve' placed into 'achirs' is 'ACHIEVERS'.
(Other definitions for achievers that I've seen before include "People who get things done" , "winners" .)