Upset since originally trapped in fly, perhaps (6)
I believe the answer is:
insect
'fly perhaps' is the definition.
(fly is a kind of insect)
'upset since originally trapped' is the wordplay.
'upset' indicates anagramming the letters.
'originally' suggests taking the first letters.
The initial letter of 'trapped' is 't'.
'since' anagrammed gives 'insec'.
'insec'+'t'='INSECT'
'in' acts as a link.
(Other definitions for insect that I've seen before include "Eg, beetle or fly" , "Small animal with six legs" , "may be attracted to a website?" , "Contemptible person" , "Small air-breathing arthropod" .)