Insisted on staff having day in action (8)
I believe the answer is:
demanded
'insisted on' is the definition.
(I've seen this in another clue)
'staff having day in action' is the wordplay.
'staff' becomes 'man' (as in staffing or manning a particular place).
'having' means one lot of letters go next to another.
'day' becomes 'd' (abbreviation for day).
'in' means one lot of letters goes inside another.
'action' becomes 'deed' (deed is a kind of action).
'man'+'d'='mand'
'mand' going within 'deed' is 'DEMANDED'.
(Other definitions for demanded that I've seen before include "Called for" , "Insisted upon" , "Requested imperiously as if by right" , "Requested peremptorily - won't take no for an answer" , "Requested forcefully" .)