Unusually tired, yet transfixed by unnamed person’s deftness (9)
I believe the answer is:
dexterity
'deftness' is the definition.
(dexterity is a kind of deftness)
'unusually tired yet transfixed by unnamed person's' is the wordplay.
'unusually' indicates an anagram.
'transfixed by' is an insertion indicator.
'unnamed person' becomes 'x' (as in phrases like Mr X).
'tired'+'yet'='tiredyet'
'tiredyet' anagrammed gives 'deterity'.
'deterity' enclosing 'x' is 'DEXTERITY'.
(Other definitions for dexterity that I've seen before include "Sleight" , "Physical skill in handling things" , "Skill of manipulation" , "Manual skill" , "Skill in handling things, adroitness" .)