Obstinate person endlessly holding a hammer (4)
I believe the answer is:
maul
'hammer' is the definition.
(maul is a kind of hammer)
'obstinate person endlessly holding a' is the wordplay.
'obstinate person' becomes 'mule' (I've seen this before).
'endlessly' means to remove the last letter.
'holding' means one lot of letters goes inside another.
'mule' with its last letter removed is 'mul'.
'mul' enclosing 'a' is 'MAUL'.
(Other definitions for maul that I've seen before include "Loose 10 (in rugby)" , "Heavy hammer for driving piles" , "Attack fiercely, tearing the flesh" , "Ill-treat" , "Injure with claws" .)