Rule 1.10

Rule 1.10

1.10

(a)        The bat shall be a smooth, round stick not more than 2.61 inches in diameter at the thickest part and not more than 42 inches in length. The bat shall be one piece of solid wood.

NOTE: No laminated or experimental bats shall be used in a professional game (either championship season or exhibition games) until the manufacturer has secured approval from the Rules Committee of his design and methods of manufacture.

(b)        Cupped Bats. An indentation in the end of the bat up to one inch in depth is permitted and may be no wider than two inches and no less than one inch in diameter. The indentation must be free of right angles and may not contain any foreign substance.

(c)        The bat handle, for not more than 18 inches from its end, may be covered or treated with any material or substance to improve the grip. Any such material or substance that extends past the 18-inch limitation shall cause the bat to be removed from the game.

NOTE: If the umpire discovers that the bat does not conform to (c) above until a time during or after which the bat has been used in play, it shall not be grounds for declaring the batter out, or ejected from the game.

Rule 1.10(c) Comment: If pine tar extends past the 18-inch limitation, then the umpire, on his own initiative or if alerted by the opposing team, shall order the batter to use a different bat. The batter may use the bat later in the game only if the excess substance is removed. If no objections are raised prior to a bat’s use, then a violation of Rule 1.10(c) on that play does not nullify any action or play on the field and no protests of such play shall be allowed.

(d)        No colored bat may be used in a professional game unless approved by the Rules Committee.

DISCUSSION

Note the difference between an illegal bat (remove the bat) and an altered bat under Rule 6.06(d) (eject the player)

George Brett hits a home run with illegal bat. This play took place prior to the rule change. Under present rules, the batter is not out for using an illegal bat and the play stands unaffected.
http://mlb.mlb.com/video/play.jsp?content_id=3180386


HISTORY
In 1932 Goose Goslin attempted to use a bat with twelve green longitudinal stripes. It was removed from the game by the umpire before Goslin’s at bat. 

There is no limit on a bat's weight. The heaviest bat on record was used by Ed Roush and weighed 48 ounces, although Babe Ruth was rumored to have used a hickory bat early in his career that weighed 52-54 ounces.