There’s a very informative article by Victoria City Police Staff Sergeant Darren Laur titled “Ritualized Combat” that’s been reprinted in various places around the ‘net. It lists common physical attributes displayed by people along a spectrum of imminence of assault.
Assuming you cannot avoid a confrontation entirely, being able to read these precursors and developing your “when” are at the core of our self-defense training.
More good articles here.
