Selector's remarkable piece of armoury (8)
I believe the answer is:
corselet
'piece of armoury' is the definition.
(piece of medieval armour)
'selector's remarkable' is the wordplay.
'remarkable' is an anagram indicator.
'selector' anagrammed gives 'CORSELET'.
(Other definitions for corselet that I've seen before include "underwear" , "stays" , "Armour" .)