No male in demonstration, as a rule (8)
I believe the answer is:
normally
'as a rule' is the definition.
(thesaurus)
'no male in demonstration' is the wordplay.
'male' becomes 'm' (common abbreviation).
'in' means one lot of letters goes inside another.
'demonstration' becomes 'rally'.
'm' inserted inside 'rally' is 'rmally'.
'no'+'rmally'='NORMALLY'
(Other definitions for normally that I've seen before include "In the ordinary or typical way" , "In the usual or average situation" , "As a general rule" , "Naturally" , "In the usual way" .)