"Hail Asgard!" stirred up legendary swordsman (3,7)
I believe the answer is:
sir galahad
'legendary swordsman' is the definition.
(mythical knight)
'hail asgard stirred up' is the wordplay.
'stirred up' is an anagram indicator (letters get stirred up or mixed).
'hail'+'asgard'='hailasgard'
'hailasgard' with letters rearranged gives 'SIR GALAHAD'.
(Other definitions for sir galahad that I've seen before include "painting by symbolist Watts" , "paragon of virtue" .)