Hate upsetting Edward before exam (6)
I believe the answer is:
detest
'hate' is the definition.
('detest' can be a synonym of 'hate')
'upsetting edward before exam' is the wordplay.
'upsetting' says the letters should be written in reverse.
'edward' becomes 'ed'.
'before' means one lot of letters go next to another.
'exam' becomes 'test' ('test' can be a synonym of 'exam').
'ed' written backwards gives 'de'.
'de'+'test'='DETEST'
(Other definitions for detest that I've seen before include "'Loathe, abhor (6)'" , "Not like" , "Dislike intensely, think badly of" , "Cordially laothe" , "Be unable to stand" .)