Expert in some chaos (7)
I believe the answer is:
anarchy
'chaos' is the definition.
(I've seen this before)
'expert in some' is the wordplay.
'expert' becomes 'arch' (I've seen this in other clues).
'in' means one lot of letters goes inside another.
'some' becomes 'any' ('any' can be similar in meaning to 'some').
'arch' inserted within 'any' is 'ANARCHY'.
(Other definitions for anarchy that I've seen before include "Complete absence of law" , "Chaotic state" , "Lawlessness; chaos" , "without structure" , "State of lawlessness and disorder" .)