Abstruse Euro-sceptic cup running over (8)
I believe the answer is:
esoteric
'abstruse' is the definition.
(I've seen this in another clue)
'euro-sceptic cup running over' is the wordplay.
I cannot really understand how this works, but
'euro' could be 'e' (E resembles the Euro symbol) and 'e' is present in the answer.
'running' could be 'ic' (abbreviation for 'in charge') and 'ic' is present in the answer.
'over' could be 'o' (cricket abbreviation) and 'o' is located in the answer.
The remaining letters 'ster' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for esoteric that I've seen before include "unintelligible to outsiders" , "of rarefied tastes" , "Occult" , "Mysterious to all but a chosen few" , "Hard to understand" .)