Culbertson coup (4)
I believe the answer is:
slam
'culbertson coup' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for slam that I've seen before include "major contract" , "Ambitious contract" , "Shut loudly and forcibly" , "Severely criticise; shut (a door) forcefully" , "Shut hard" .)