Bird upsets no calf (6)
I believe the answer is:
falcon
'bird' is the definition.
(falcon is a kind of bird)
'upsets no calf' is the wordplay.
'upsets' is an anagram indicator.
'no'+'calf'='nocalf'
'nocalf' anagrammed gives 'FALCON'.
(Other definitions for falcon that I've seen before include "Hunter winged" , "Kestrel, for example" , "A hunting bird, may be peregine" , "Hunting bird like peregrine or merlin" , "that's seen flying" .)