Changed gear in anger (4)
I believe the answer is:
rage
'anger' is the definition.
(rage is a kind of anger)
'changed gear' is the wordplay.
'changed' is an anagram indicator.
'gear' with letters rearranged gives 'RAGE'.
'in' is the link.
(Other definitions for rage that I've seen before include "Temper - fashion" , "Fury, passion" , "Fad or anger" , "Be furious" , "Latest fashion; high emotion" .)