Exxon Valdez mishap (5)
I believe the answer is:
spill
'exxon valdez mishap' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for spill that I've seen before include "Cause liquid to flow from a container" , "to make light of?" , "Accidentally cause to overflow" , "Upset - lighter" , "Cause liquid to overflow" .)