Half the agency come out before the crisis (9)
I believe the answer is:
emergency
'the crisis' is the definition.
(emergency is a kind of crisis)
'half the agency come out before' is the wordplay.
'half the' means to take half the letters.
'come out' becomes 'emerge' (synonyms).
'before' means one lot of letters go next to another.
'agency' with half the letters taken is 'ncy'.
'ncy' after 'emerge' is 'EMERGENCY'.
(Other definitions for emergency that I've seen before include "Sudden occurrence necessitating urgent action" , "Occurrence demanding immediate remedy" , "Crisis requiring immediate action" , "Serious situation needing prompt action" , "Serious casualty" .)