Edgar, when upset, was very angry (5)
I believe the answer is:
raged
'very angry' is the definition.
I can't judge whether this defines the answer.
'edgar when upset' is the wordplay.
'when upset' indicates an anagram.
'edgar' with letters rearranged gives 'RAGED'.
'was' acts as a link.
Can you help me to learn more?
(Other definitions for raged that I've seen before include "Behaved violently" , "Was violently angry" , "seethed" , "Showed violent anger" , "Fumed" .)