Mover and shaker upset many in party (6)
I believe the answer is:
dynamo
'mover and shaker' is the definition.
I can't tell whether this defines the answer.
'upset many in party' is the wordplay.
'upset' is a reversal indicator.
'in' means one lot of letters goes inside another.
'party' becomes 'do' (do can informally mean a party).
'many' back-to-front is 'ynam'.
'ynam' placed into 'do' is 'DYNAMO'.
Can you help me to learn more?
(Other definitions for dynamo that I've seen before include "One creating electricity" , "Small generator" , "Source of electric current" , "Energy converter - hard worker" , "Electricity generator or energetic person" .)