A tag that upsets Bella (5)
I believe the answer is:
label
'a tag' is the definition.
(I've seen this before)
'upsets bella' is the wordplay.
'upsets' indicates anagramming the letters.
'bella' is an anagram of 'LABEL'.
'that' acts as a link.
(Other definitions for label that I've seen before include "Tag or designation" , "Mark" , "Put a name to" , "Identify" , "Descriptive tag" .)