That poor fathead moved without preliminaries (2,3,4,2,1,3)
I believe the answer is:
at the drop of a hat
'without preliminaries' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'that poor fathead moved' is the wordplay.
'moved' is an anagram indicator.
'that'+'poor'+'fathead'='thatpoorfathead'
'thatpoorfathead' with letters rearranged gives 'AT THE DROP OF A HAT'.
Can you help me to learn more?
(Other definitions for at the drop of a hat that I've seen before include "Immediately" , "instantly" , "suddenly?" , "When pork pie downed" , "in no time at all" .)