The third in a series from Adam Plantinga’s 400 Things Cops Know: Street-Smart Lessons from a Veteran Patrolman:
People give off plenty of indicators that they’re looking to fight. Some precursors are obvious, like the clenched fists and the readjustment of the feet into an attack stance. Others are more subtle, like the lowering of the chin to instinctively protect their neck, or the rigid setting of the jaw or brow. Some people dry their hands on their pants to prep themselves for an assault. Many of these indicators are reflexive. People don’t even know they’re doing them. They’re tells, like poker players have. So it helps to pay attention to these signs and signals because if you see them coming from the guy you’re about to arrest, take your baton out and call for backup, because he’s not going quietly. He’s going to make you work for it.
Good to cover this subject. Police and others that have to counter human aggression should be trained to understand how people move from anxiety to aggression.
I see the fist clenching (or just opening and closing of hands) all of the time and I'll even tell people, "hey, stop clenching your fists, I'm not here to fight you." Sometimes this catches them off guard and they de-escalate a bit. I try to get them back into anxiety (typical signs are pacing, wringing of hands, increased respiratory rate, etc)before they make that leap to putting their hands on someone. It doesn't work for everyone, of course, but its worth a try.