Energetic person upset a lot in party (6)
I believe the answer is:
dynamo
'energetic person' is the definition.
(I've seen this before)
'upset a lot in party' is the wordplay.
'upset' says the letters should be written backwards.
'a lot' becomes 'many' (**).
'in' is an insertion indicator.
'party' becomes 'do' (do is a kind of party).
'many' backwards is 'ynam'.
'ynam' inserted into 'do' is 'DYNAMO'.
(Other definitions for dynamo that I've seen before include "something electrifying" , "Machine" , "Small generator" , "Juice supplier" , "Electric current producer" .)