As children get older, this incidental outdoor activity--say, while waiting to be called to eat--becomes less bumptious, physically and entails more loitering with others, sizing people up, flirting, talking, pushing, shoving and horseplay. Adolescents are always being criticized for this kind of loitering, but they can hardly grow up without it. The trouble comes when it is done not within society, but as a form of outlaw life.

The requisite for any of these varieties of incidental play is not pretentious equipment of any sort, but rather space at an immediately convenient and interesting place. The play gets crowded out if sidewalks are too narrow relative to the total demands put on them. It is especially crowded out if the sidewalks also lack minor irregularities in building line. An immense amount of both loitering and play goes on in shallow sidewalk niches out of the line of moving pedestrian feet.

Jane Jacobs