Boxer who sat up, befuddled (8)
I believe the answer is:
southpaw
'boxer' is the definition.
(term for a left-handed boxer)
'who sat up befuddled' is the wordplay.
'befuddled' indicates an anagram.
'who'+'sat'+'up'='whosatup'
'whosatup' with letters rearranged gives 'SOUTHPAW'.
(Other definitions for southpaw that I've seen before include "Left-hander" , "Boxer leading with right hand" , "Unorthodox leader" , "Boxer who leads with right fist" , "Right leader" .)