Defence starts at a boundary. When anger flares, something has been read as crossing a line, so the question worth asking is which line.

What the research says

Experimental work comparing negative states found that regret, guilt, shame, anger and sadness are experienced as distinct, with different appraisals behind each, which supports the effort of naming precisely what happened rather than settling for upset. Precision here is practical rather than fussy. These were controlled comparisons of experience and not studies of how people state boundaries.

Strength of evidence: one line of research. A single study, or a theoretical account.