Rules chap could make assistant referee (8)
I believe the answer is:
linesman
'assistant referee' is the definition.
(I know that assistant referee can be written as linesman)
'rules chap' is the wordplay.
'rules' becomes 'lines' (I've seen this in another clue).
'chap' becomes 'man' (chap can mean a man).
'lines'+'man'='LINESMAN'
'could make' acts as a link.
(Other definitions for linesman that I've seen before include "Official helping referee - telephone repairer" , "sports official" , "Referee's assistant" , "park official" , "Male official with a flag" .)