It's an audience sitting on the unofficial "rooftop bleachers" of rowhouses outside of Shibe Park in Philadelphia. They are watching the first game in the 1914 World Series between Boston Braves and Philadelphia Athletics.
Shibe Park, opened in 1909, was the first steel-and-concrete stadium in professional baseball. At first, it was located in a poorer section of the city, but the surrounding neighborhoods grew as the stadium drew regular crowds. Importantly, row houses along 20th street turned out to be great places to watch games for free. As the Wikipedia author for the entry on Shibe Park states,
The numbers involved in this cottage industry were considerable: a rooftop bleacher could hold up to 80 people, with 18 more in the bay window of the front bedroom and more even on the porch roof. Viewers on the block could number up to several thousand for important games. Housewives served up refreshments for sale and children scurried to the hot dog vendors on the street, bought dogs for a nickel, and brought them back to sell for a dime. With so much money on the line, the business got organized and formalized very quickly; homeowners were quickly squeezed for bribes by city amusement tax collectors, and city police collected commissions for collaring and herding fans from the sidewalk into particular homes.
If that wasn't interesting enough, it soon turned into a story about disciplining of audiences. One interesting things about putting a ballpark in a city is that the park's physical boundaries can be expanded easily by audience members. The infrastructure of the city itself can temporarily become part of the stadium, something that not only expands the audience but also expands the definition of the game--it becomes not just a discrete sporting event but a wider civic occasion. Of course, not everyone will be pleased by such a prospect, especially not the people attempting to commodify the event. In 1934, the finally fed-up owners of the Athletics, Ben Shibe and Connie Mack, installed a high fence that purposefully blocked the views from the street. It became known as the "spite fence," forcing anyone who wanted to participate in a game to buy a ticket.
I always thought that walled enclosures around sporting stadiums were for keeping intact the integrity of the gameplay from the chaos of everyday life in the surrounding area, and secondarily, for holding up the upper balconies of a stadium. Turns out they might have another function: protecting profits.
More images of Shibe Park can be found at the The Baseball Chronicle.