Some have ruined state (4)
I believe the answer is:
aver
'state' is the definition.
(both can mean to declare)
'some have ruined' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'AVER' can be found hidden inside 'have ruined'.
(Other definitions for aver that I've seen before include "Prove to be true" , "Formally assert" , "Declare < old cattle" , "State firmly, propound" , "Say firmly, rave if necessary" .)