Those old revolutionary guards one's blasting (5)
I believe the answer is:
noisy
'blasting' is the definition.
(thesaurus)
'those old revolutionary guards one's' is the wordplay.
'those old' becomes 'yon' (archaic pronoun equivalent to 'those').
'revolutionary' shows that the letters should be reversed in order.
'guards' means one lot of letters goes inside another.
'one's' becomes 'is' (Roman numeral).
'yon' reversed gives 'noy'.
'noy' placed around 'is' is 'NOISY'.
(Other definitions for noisy that I've seen before include "Disturbingly loud" , "Full of disturbing sounds" , "Clamorous" , "Rowdy" , "row" .)