Upsetting giant - gait was wrong (9)
I believe the answer is:
agitating
'upsetting' is the definition.
(agitating is a kind of upseting)
'giant gait was wrong' is the wordplay.
'was wrong' indicates anagramming the letters (I've seen 'is wrong' mean this).
'giant'+'gait'='giantgait'
'giantgait' with letters rearranged gives 'AGITATING'.
(Other definitions for agitating that I've seen before include "stirring things up" , "Shaking" , "Disturbing" .)