Nowadays three to four dozen baseballs are used in the average Major League baseball game. Until 1920, only two or three balls were used. But on Aug. 16, 1920, Ray Chapman, who was batting for the Cleveland Indians, was hit in the temple by a ball pitched by the New York Yankees' Carl Mays. Chapman died the next day.
The baseball that hit Chapman was so dirty from play that people said he couldn't see it well enough to get out of the way. So today, scuffed balls, dirty balls, even ones that just don't feel right to the pitcher are tossed out.