Found upside down in field, dirty puzzle (6)
I believe the answer is:
riddle
'puzzle' is the definition.
(riddling is a kind of puzzling)
'found upside down in field dirty' is the wordplay.
'upside down' says the letters should be written backwards.
'found' indicates a hidden word.
'elddir' is hidden within 'in field dirty'.
'elddir' back-to-front is 'RIDDLE'.
(Other definitions for riddle that I've seen before include "Perforate with gunshot - poser" , "It may have an answer" , "Puzzling question - sieve" , "Screen" , "Sieve; enigma" .)