Change gear in fury (4)
I believe the answer is:
rage
'fury' is the definition.
(I know that fury can be written as rage)
'change gear' is the wordplay.
'change' indicates anagramming the letters.
'gear' anagrammed gives 'RAGE'.
'in' acts as a link.
(Other definitions for rage that I've seen before include "Fit of anger" , "Be furious" , "Extreme anger" , "Fury - fashion" , "Craze, fad" .)