home-run balls hit against the Chicago Cubs when playing at Wrigley Field). Moreover, baseballs are replaced on a regular interval during the course of a game. Major League Baseball requires the home team to supply the baseballs that will be used during that day's games. MLB further require that the home team make available at least 90 new baseballs to the umpires prior to the start of the game. Generally, a baseball is replaced every time it either is hit by a batter or touches the ground. In a typical Major League Baseball game, baseballs are replaced every five pitches or so with a total game average of around 70 baseballs being used. Because baseball hitting is difficult, baseball rules prohibit the deliberate scratching or scuffing of a ball, or the application of any foreign substance that could conceivably affect the flight or visibility of a ball. Balls that are deliberately made more difficult to hit by applying foreign substances are often known as spitballs, regardless of the specific substance applied (such as Vaseline). Both spitballs and those that become scuffed or scratched through normal game play are immediately removed from play and never reused. The current rules regarding the condition of baseballs did not come into effect until 1920, after the death of Ray Chapman from being hit with a Carl Mays spitball. Before that point, the rules were similar to those still present in cricket. However, the new rules were not consistently enforced for several decades afterwards, and several pitchers (most notably Gaylord Perry) built careers around skirting these rules, doing such things as hiding nail files in their gloves or putting Vaseline on the underside of the peaks of their caps. In modern baseball, however, the prohibition against modifying the baseball in almost any way is strictly enforced and players found to be in violation of this rule are not only ejected from the game in which the infraction occurred, but are also subject to a suspension. The only substance applied to a baseball is the Delaware River mud formula that umpires rub in before a game to remove the "shine" from the ball and improve its grip. The pitcher is also allowed to use rosin on his hands (via a rosin bag) to improve his grip, and to blow on his hands in cold weather. Gameplay Theoretically, in baseball, a single pitcher can throw every pitch