That space doesn’t seem big enough for a baseball field. It’s only about 50 ft. wide, and maybe 60-70 ft. long, accounting for the angle of the north border. If anyone hit baseballs there, they would smash into a lot of the parked or moving cars on Virginia Ave. They could also hit foul balls back into the Fed building unless someone added a metal cage. I doubt the Fed or their friends would let that happen.
[For those who don’t know, it’s Edward J. Kelly Park, directly behind the Federal Reserve building. I thought it was part of the Fed but I think it might be administered by the National Park Service. There are other sculptures in the park. Not a lot of info online. According to the Wall Street Journal, NPS owns the tennis court there, but the Fed administers it. At least they did in 2012.]
http://blogs.wsj.com/economics/2012/06/22/qe-anyone-inside-the-feds-little-known-tennis-court/