Barge in, upset at charges (9)
I believe the answer is:
gatecrash
'barge in' is the definition.
(synonyms)
'upset at charges' is the wordplay.
'upset' is an anagram indicator.
'at'+'charges'='atcharges'
'atcharges' with letters rearranged gives 'GATECRASH'.
(Other definitions for gatecrash that I've seen before include "join party unofficially" , "to do so uninvited" , "join party if not wanted" , "Try to get in for free" , "enter without invitation" .)