Rule 6.03(a)(4):

The following policies are in effect in regard to corked, improperly treated, and otherwise altered bats:
First, Official Baseball Rules 3.02(a) through (d) and 6.03(a)(4) are in no way changed or affected by the policies set forth herein. These rules, which define the construction of the bat, the use of substances to improve the grip of the bat and the penalty for the use of an illegal bat, remain in effect.
Second, the policy regarding one challenge per game for each team of an opposing team’s bat shall remain in effect. Therefore, if a manager suspects an opposing player of using or attempting to use a corked or improperly treated or altered bat, the manager may request the umpire crew chief to inspect and impound the bat. If the umpire’s visual inspection reveals no irregularities, the bat will be further examined either in the city where the game is played or at the Commissioner’s Office. Each manager is limited to making this request one time per game. The request must be made either just prior to or just after the batter has batted. The actual process of batting will not be interrupted. Notwithstanding the manager’s right to one challenge per game, the umpires may at any time during the game or before or after a game inspect and/or impound a bat or bats for testing. If exercised during a game, such action by an umpire may be in addition to the challenge rights of a manager.
Third, should it be discovered by direct, immediate observation by an umpire during play that a player is using or attempting to use an illegal bat, the provisions of Official Baseball Rule 6.03(a)(4) will fully apply and will result in the ejection of the player and in nullification of any game action immediately attributable to the use of that bat.
Fourth, should it be found that an illegal bat was used in the game, the player using an illegal bat, his manager and perhaps his Club will all be liable to severe discipline, including fines and suspension as the Commissioner’s Office may determine.

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