Lawman's family enthralled by member of the clergy (9)
I believe the answer is:
parkinson
'lawman's' is the definition.
(C Northcote Parkinson devised 'Parkinson's law')
'family enthralled by member of the clergy' is the wordplay.
'family' becomes 'kin' (synonyms).
'enthralled by' is an insertion indicator ('enthral' can mean 'capture').
'member of the clergy' becomes 'parson' (parson is a type of clergyman).
'kin' put into 'parson' is 'PARKINSON'.
(Other definitions for parkinson that I've seen before include "C. Northcote ---, writer, historian (---'s Law)" , "[LAWMAKER]?" , "Man of the law" , "Lawman" .)