Ross: Balls that come in contact with the infield dirt are usually replaced because the scuffed cover can sometimes give a pitched ball unusual movement, like a breaking ball thrown with a certain grip. The dirt has a harder, spongy texture so balls that spin into the dirt get scuffed. A tiny crack on a seam can be a big advantage for pitchers. It's funny to see an umpire take a ball from the catcher and give it right back without telling him. Used baseballs are saved for batting practice or donated to schools.

Source: Los Angeles Times August 30, 2018 15:00 UTC