I err badly, upsetting worm-catcher (5,4)
I believe the answer is:
early bird
'catcher' is the definition.
(the early bird catches the worm)
'i err badly upsetting' is the wordplay.
'upsetting' is an anagram indicator.
'i'+'err'+'badly'='ierrbadly'
'ierrbadly' with letters rearranged gives 'EARLY BIRD'.
'worm' acts as a link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for early bird that I've seen before include "One up with the lark" , "arrived before time" , "Archaeopteryx, say" , "communications satellite!" , "One who rises before others" .)