Pale sort of request (4)
I believe the answer is:
plea
'request' is the definition.
(I know that plea is a type of appeal)
'pale sort' is the wordplay.
'sort' indicates an anagram.
'pale' with letters rearranged gives 'PLEA'.
'of' is the link.
(Other definitions for plea that I've seen before include "Guilty perhaps" , "Excuse - pretext" , "suit" , "Leap (anag.)" , "Appeal - with bargaining?" .)