R.A.Stone managed to show disloyalty (7)
I believe the answer is:
treason
'disloyalty' is the definition.
(I know that treason is a type of disloyalty)
'r a stone managed' is the wordplay.
'managed' indicates an anagram.
'r'+'a'+'stone'='rastone'
'rastone' with letters rearranged gives 'TREASON'.
'to show' is the link.
(Other definitions for treason that I've seen before include "Deliberate act of betrayal" , "attempting to overthrow the king" , "One's art? (anag)" , "Betrayal of one's nation" , "Betrayal (of one's country)" .)