Put in danger protecting a royal (8)
I believe the answer is:
imperial
'royal' is the definition.
('imperial' can be a synonym of 'royal')
'put in danger protecting a' is the wordplay.
'put in danger' becomes 'imperil' ('imperil' can be a synonym of 'endanger').
'protecting' is an insertion indicator.
'imperil' enclosing 'a' is 'IMPERIAL'.
(Other definitions for imperial that I've seen before include "Majestic, like UK gallon" , "Mint --, sweet" , "Magnificent; small pointed beard" , "I prime Al to describe the rule of great territories" , "Non-metric" .)