Party starts out fun, like other voluntary events, and is undertaken for pleasure, not reward (6,2,4)
I believe the answer is:
labour of love
'is undertaken for pleasure not reward' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'party starts out fun like other voluntary events' is the wordplay.
'party' becomes 'labour' (Labour Party is an example).
'starts' indicates taking the first letters.
The first letters of 'out fun like other voluntary events' is 'oflove'.
'labour'+'oflove'='LABOUR OF LOVE'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for labour of love that I've seen before include "One not undertaken for advantage" , "Task undertaken for enjoyment" , "Task done for pleasure not money" , "Work performed voluntarily without hope of material reward" , "Task one enjoys" .)