Study by fans upset and astonished (7)
I believe the answer is:
stunned
'astonished' is the definition.
(synonyms)
'study by fans upset' is the wordplay.
'study' becomes 'den' (term for a study or office).
'by' says to put letters next to each other.
'fans' becomes 'nuts' (both can mean enthusiasts).
'upset' says the letters should be written backwards.
'den'+'nuts'='dennuts'
'dennuts' reversed gives 'STUNNED'.
'and' is the link.
(Other definitions for stunned that I've seen before include "Dazed; astounded" , "Knocked out; astonished" , "Knocked unconscious" , "Stupefied" , "Taken aback" .)