Risky to upset old royal supporter (7)
I believe the answer is:
yorkist
'old royal supporter' is the definition.
(supporter of the House of York)
'risky to upset' is the wordplay.
'upset' is an anagram indicator.
'risky'+'to'='riskyto'
'riskyto' anagrammed gives 'YORKIST'.
(Other definitions for yorkist that I've seen before include "Supporter wearing white rose" , "White rose wearer" , "Plantagenet?" , "Civil war protagonist" , "he's no supporter of the red rose" .)