A lot of CCTV footage of violence shows initial verbal altercation that turns physical. The perpetrators abandon words due to lack of verbal skills and general violent drunk or 'gangsta-wanna-be' nature. Victims too, often miss the opportunity to walk away, misreading the situation by running their mouths.
Street smart is about reading the situation, like defensive driving. 3AM Sunday morning as you walk home, awareness of you surroundings at all times is smart - also fun and challenging and just good way to be. Doesn't have to mean "guard up", it just means not careless.
