The young robin either jumped or was blown from his nest when a fierce August thunderstorm hit overnight. The jumpling hunkered down on the sidewalk for the next 24 hours, a nerve-wracking period for nearby humans. But he made it, with a little help from his friends, and a lot of feeding by his parents.
When it started getting hot in the sun a little later, the young robin hopped off into the shadows of some nearby bushes, leaving behind a little patch of 30-some white polka dots as record of its stay on the sidewalk.
That evening, the little bird made a cameo appearance in the middle of the street, but was soon herded to safety by a meddling human. Getting run over by a car is not letting Nature take its course, methinks.
As their wings are not yet fully developed, fledgling robins usually don't fly that well when they leave the nest, and most don't go much more than 20-30 meters or so on their maiden flight. Many make it to an elevated perch, but some end up on the ground - a familiar springtime sight in many parts of the United States and N. America, where these birds are wide-spread and well-loved.
As we can see here, the fledgling American Robin's wings and tail are still quite short at this stage. Like many fledglings, they tend to hunker down and stay put after their initial foray, but can hop around, if necessary, pretty well. By hook or crook, those on the ground that aren't immediately snatched up by cats or other predators soon manage to fly up to a safer perch, where they continue to be fed by their parents for several days, or longer. The wings and tail grow rapidly once the young thrush is out of the nest, but the head and breast feathers remain much as seen here.
Note how the young robin's feet and beak are almost adult sized.