Anger of armchair expert (3)
I believe the answer is:
ire
'anger' is the definition.
(ire is intense rage)
'of armchair expert' is the wordplay.
'of' indicates the answer is hidden within the clue.
'IRE' is hidden within 'armchair expert'.
(Other definitions for ire that I've seen before include "'Anger, wrath (3)'" , "Losing head" , "heat" , "passionate feeling" , "Outrage" .)