Creakiest sort of athlete (3-6)
I believe the answer is:
ice-skater
'athlete' is the definition.
(I've seen this before)
'creakiest sort' is the wordplay.
'sort' indicates anagramming the letters.
'creakiest' is an anagram of 'ICE-SKATER'.
'of' is the link.
(Other definitions for ice-skater that I've seen before include "Dean for one" , "One gliding over rink" , "Winter sportsperson" , "Torvill or Dean, say" , "Person gliding on frozen water" .)