Flounder for the party (6)
I believe the answer is:
thrash
'party' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for thrash that I've seen before include "Administer severe beating to" , "wild party" , "Beat hard" , "Beat heavily, perhaps with whip" , "Trounce, beat soundly" .)