Friend crashing rave causes commotion (7)
I believe the answer is:
palaver
'commotion' is the definition.
(I've seen this before)
'friend crashing rave causes' is the wordplay.
'friend' becomes 'pal' (pal can mean a friend).
'crashing' indicates putting letters inside (inserted letters crash into another word).
'causes' indicates anagramming the letters.
'rave' with letters rearranged gives 'aver'.
'pal' inserted inside 'aver' is 'PALAVER'.
(Other definitions for palaver that I've seen before include "idle conversation" , "Fuss and bother" , "Yak" , "Kind of discussion or idle chatter" , "(Talk of a) conference" .)