Regular customer, Dad, right about cricket side (6)
I believe the answer is:
patron
'regular customer' is the definition.
(I've seen this in another clue)
'dad right about cricket side' is the wordplay.
'dad' becomes 'pa' (both can mean one's father).
'right' becomes 'rt' (abbreviation as in Rt Hon- the Right Honourable).
'about' says the letters should be written backwards.
'cricket side' becomes 'on' (cricket term, on or leg side).
'rt' back-to-front is 'tr'.
'pa'+'tr'+'on'='PATRON'
(Other definitions for patron that I've seen before include "With help, he" , "One gives financial or other support, to an artist say" , "One who protects" , "Saint" , "Patrick for Ireland, for example" .)