According to a 2004 study by physicist David Kagan of California State University at Chico, keeping the balls at 50 percent relative humidity lowers their coefficient of restitution, a.k.a. bounciness. This means that the balls don't bounce off the bat as powerfully as dried-out ones do.

TV footage that went viral caught Giants ace Tim Lincecum profanely expressing suspicions about one of the balls he rejected in the sixth inning Friday night -- as he was throwing perfect ball for seven of his eight innings in a 2-1 victory over the Rockies. The Giants had already expressed concerns in a call to MLB prior to this series, although they said they didn't file an official complaint.

"They definitely called us on this," Pat Courtney, MLB senior vice president of public relations, said on Saturday. "That's why we made the changes we did."

Umpires will witness the balls being removed from "the humidor," the temperature- and atmospheric pressure-controlled chamber; watch them as they're taken to the field; and be able to see them at all times. The baseballs have been kept in a bag near the Rockies' dugout during play.