To some degree, Sir Walter fails to finish The Talisman (6)
I believe the answer is:
mascot
'the talisman' is the definition.
('mascot' can be a synonym of 'talisman')
'to some degree sir walter fails to finish' is the wordplay.
'to some degree' becomes 'MA' (Master of Arts is a type of degree).
'sir walter' becomes 'scott' (I've seen this in another clue).
'fails to finish' means to remove the last letter.
'scott' with its final letter removed is 'scot'.
'ma'+'scot'='MASCOT'
(Other definitions for mascot that I've seen before include "Good-luck charm" , "Team's good-luck bringer" , "'Symbol, for a team say (6)'" , "Team's good luck bringer" , "World Cup Willie, say" .)