Emergency rules I -- Sir Chris -- will hold over (6)
I believe the answer is:
crisis
'emergency' is the definition.
(a crisis is an emergency)
'rules i sir chris will hold over' is the wordplay.
'hold' indicates the answer is hidden within the clue (I've seen 'holding' mean this).
'over' says the letters should be written in reverse.
'sisirc' is hidden in the letters of 'rules i sir chris will'.
'sisirc' written backwards gives 'CRISIS'.
(Other definitions for crisis that I've seen before include "Desperate situation" , "Time of severe difficulty" , "A decisive or dangerous time" , "Time of sever difficulty" , "Climacteric" .)