Cruel one downcast before it's adjusted (6)
I believe the answer is:
sadist
'cruel one' is the definition.
(I've seen this in another clue)
'downcast before it's adjusted' is the wordplay.
'downcast' becomes 'sad' (I've seen this in another clue).
'before' says to put letters next to each other.
'adjusted' is an anagram indicator.
'its' anagrammed gives 'ist'.
'sad'+'ist'='SADIST'
(Other definitions for sadist that I've seen before include "One gaining pleasure from inflicting pain on another" , "One enjoying inflicting pain" , "'Tis sad s/he likes to inflict pain" , "One who takes pleasure in cruelty" , "Person who likes to inflict pain" .)