Vaults to mix chaser (6)
I believe the answer is:
arches
'vaults' is the definition.
(I've seen this before)
'mix chaser' is the wordplay.
'mix' indicates an anagram.
'chaser' anagrammed gives 'ARCHES'.
'to' acts as a link.
(Other definitions for arches that I've seen before include "Extends across" , "Search (anag.)" , "Curves over openings" , "Curved parts of foot, sometimes fallen" , "Parts of bridge structure" .)