Knowledgeable about heraldry, is peeved (2,2,4)
I believe the answer is:
up in arms
'knowledgeable' is the definition.
I know nothing about this answer so I can't tell whether this works.
'heraldry is peeved' is the wordplay.
I cannot quite understand how this works, but
'heraldry' could be 'arms' (arms is a kind of heraldry) and 'arms' is found within the answer.
This explanation may well be incorrect...
'about' is the link.
Can you help me to learn more?
(Other definitions for up in arms that I've seen before include "Openly protesting" , "being angry" , "Outraged" , "Rioting" , "Indignant" .)