Person working out tax without hesitation, right? (9)
I believe the answer is:
exerciser
'person working out' is the definition.
(I've seen this before)
'tax without hesitation right?' is the wordplay.
'tax' becomes 'excise' (excise is a kind of tax).
'without' is an insertion indicator ('without' can be similar in meaning to 'outside').
'hesitation' becomes 'er' (sound made while hesitating - um, er).
'right?' becomes 'r' (abbreviation).
'excise' enclosing 'er' is 'exercise'.
'exercise'+'r'='EXERCISER'
(Other definitions for exerciser that I've seen before include "Gym member" , "swimmer, perhaps" , "Fitness fanatic" , "Person working out" , "Device helping strengthen muscles" .)