Expand case cracked after deadline (8)
I believe the answer is:
escalate
'expand' is the definition.
(thesaurus)
'case cracked after deadline' is the wordplay.
'cracked' indicates anagramming the letters.
'after deadline' becomes 'late' (I've seen this in another clue).
'case' with letters rearranged gives 'esca'.
'esca'+'late'='ESCALATE'
(Other definitions for escalate that I've seen before include "Increase in magnitude" , "Ramp up" , "Magnify" , "Increase in extent or intensity (8)V" , "mount in tension" .)