Pot or goblet perhaps changing hands (5)
I believe the answer is:
grass
'pot' is the definition.
(cannabis)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for grass that I've seen before include "often walked over in court" , "Vegetation; informer" , "drugs" , "blades" , "What meadowlark perches on" .)