Loot harbour, causing misery (10)
I believe the answer is:
spoilsport
'misery' is the definition.
(thesaurus)
'loot harbour' is the wordplay.
'loot' becomes 'spoils'.
'harbour' becomes 'port' (I've seen this before).
'spoils'+'port'='SPOILSPORT'
'causing' is the link.
(Other definitions for spoilsport that I've seen before include "Party-pooper" , "Person marring others' pleasure" , "One who ruins others' enjoyment" , "One who won't play?" , "Wet blanket" .)