Dave in an upset state (6)
I believe the answer is:
nevada
'state' is the definition.
(I know that Nevada is a state)
'dave in an upset' is the wordplay.
'in' indicates putting letters inside.
'upset' says the letters should be written backwards.
'dave' going within 'an' is 'adaven'.
'adaven' backwards is 'NEVADA'.
(Other definitions for nevada that I've seen before include "American state, capital Carson City" , "Arid US state" , "Western US state" , "Curiously, Dan and Eva are in the US" , "US state, capital Carson City" .)