Rule initially covering a new cricket side (5)
I believe the answer is:
canon
'rule' is the definition.
(canon can mean a law)
'initially covering a new cricket side' is the wordplay.
'initially' suggests taking the first letters.
'new' becomes 'n' (abbreviation as in New Testament NT).
'cricket side' becomes 'on' (cricket term, on or leg side).
The initial letter of 'covering' is 'c'.
'c'+'a'+'n'+'on'='CANON'
(Other definitions for canon that I've seen before include "Round, general rule" , "senior cleric" , "Rule -- principle" , "General rule; clergyman" , "religious leader" .)