Upset at charges? Get in free! (9)
I believe the answer is:
gatecrash
'in free' is the definition.
Although both the answer and definition are verbs in their base form, I don't see how they can define each other.
'upset at charges?' is the wordplay.
'upset' indicates an anagram.
'at'+'charges'='atcharges'
'atcharges' anagrammed gives 'GATECRASH'.
'get' acts as a link.
Can you help me to learn more?
(Other definitions for gatecrash that I've seen before include "join party if not wanted" , "to do so uninvited" , "Try to get in for free" , "join party unofficially" , "enter without invitation" .)