To sponsor a protege is retrogressive
I believe the answer is:
backward
'retrogressive' is the definition.
(thesaurus)
'to sponsor a protege' is the wordplay.
'to sponsor' becomes 'back'.
'a protege' becomes 'ward'.
'back'+'ward'='BACKWARD'
'is' is the link.
(Other definitions for backward that I've seen before include "Bashful - in reverse" , "Direction to the rear" , "not very bright" , "Retiring" , "Directed to the rear" .)