Excellent European breeding ground: limited measure going out the window (14)
I believe the answer is:
defenestration
'going out the window' is the definition.
(to defenestrate is to throw out of a window)
'excellent european breeding ground limited measure' is the wordplay.
'excellent' becomes 'def' (old-fashioned term for excellent).
'european' becomes 'E' (abbreviation e.g. EU).
'breeding ground' becomes 'nest' (I've seen this in other clues).
'limited measure' becomes 'ration' (a limited or rationed quantity).
'def'+'e'+'nest'+'ration'='DEFENESTRATION'
(Other definitions for defenestration that I've seen before include "Act of ejecting someone through a window" , "Act of throwing out of a window" , "projected through lights" , "Opening extraction" , "Ejection from a window" .)