Understanding the Area Behind the Pitcher's Mound

Question
what is the box like thing just behind and to the right of the pitchers mound?

Answer
Lee,

If you can be a little more specific I could help a little better.  The only thing that is allowed behind the pitchers mound is usually a rosin bag and sometimes you may see a small rubber mat that players can clean their spikes off with during rainy and muddy games.

Hope this helps,
John Priest