Alarming shifts, disputable (8)
I believe the answer is:
marginal
'disputable' is the definition.
(thesaurus)
'alarming shifts' is the wordplay.
'shifts' indicates anagramming the letters.
'alarming' with letters rearranged gives 'MARGINAL'.
(Other definitions for marginal that I've seen before include "unsafe seat" , "Alarming (anag) - too small to matter" , "On the edges of" , "Borderline" , "on border" .)