Loyalist beginning to pontificate at uprising (7)
I believe the answer is:
patriot
'loyalist' is the definition.
(thesaurus)
'beginning to pontificate at uprising' is the wordplay.
'beginning to' indicates taking the first letters.
'uprising' becomes 'riot' (I've seen this before).
The first letter of 'pontificate' is 'p'.
'p'+'at'+'riot'='PATRIOT'
(Other definitions for patriot that I've seen before include "Nationalist" , "One loving their country" , "One who loves his or her country" , "Country lover" , "One defends his country" .)