Foreshadows a stoppage in the docks (8)
I believe the answer is:
portends
'foreshadows' is the definition.
('portend' can be a synonym of 'foreshadow')
'a stoppage in the docks' is the wordplay.
'a stoppage' becomes 'end' (I've seen this in another clue).
'in the' is an insertion indicator.
'docks' becomes 'ports' (I am not sure about this - if you are sure you should believe this answer much more).
'end' going inside 'ports' is 'PORTENDS'.
Can you help me to learn more?
(Other definitions for portends that I've seen before include "Gives warning" , "Signals" , "Indicates by signs" , "Augurs, bodes" , "Warns" .)