The way of a showman (3)
I believe the answer is:
how
'the way' is the definition.
'of a showman' is the wordplay.
'of' says the answer is hidden in the clue.
'HOW' is hidden in the letters of 'showman'.
(Other definitions for how that I've seen before include "Who (anag.)" , "See 16" , "In what way?" , "By what means?" , "In what manner or method?" .)