Who am I?

I am hard and I am brown. I usually get hit by the ball. If they bunt it does not hurt, but sometimes they break me. I get thrown to the ground sometimes. When I end up in the dirt, they run away from me. I can never stay clean, because they are always dropping me on the ground and the players’ hands are dirty which when they grab me they get me dirty. My job is to hit the ball in the gaps on the field. Without me, the game of baseball is not the same. Who am I?