UFO? Clay pigeon perhaps! (6,6)
I believe the answer is:
flying saucer
'ufo?' is the definition.
('flying saucer' can be a synonym of 'ufo')
I can't explain the rest of the clue.
(Other definitions for flying saucer that I've seen before include "Extraterrestrial visitor" , "observed when bull enters china shop?" , "UFO?" , "Phenomenon" .)