Was angry getting the wrong grade (5)
I believe the answer is:
raged
'was angry' is the definition.
'the wrong grade' is the wordplay.
'the wrong' indicates anagramming the letters.
'grade' anagrammed gives 'RAGED'.
'getting' is the link.
(Other definitions for raged that I've seen before include "Expressed intense anger" , "Flipped one's lid" , "seethed" , "Spoke loudly and angrily" , "was having fits" .)