Shrewd piece of vaulting (4)
I believe the answer is:
arch
I believe this is a triple definition!
'shrewd' is the first definition.
(I've seen this before)
'piece' is the second definition.
(arch is a kind of piece)
'of' is a link.
'vaulting' is the third definition.
(thesaurus)
(Other definitions for arch that I've seen before include "Cunning; playful" , "spanner" , "Roguish, teasing" , "Mysterious - curve" , "Mischievous - curve" .)