Rule 1.14

Rule 1.14

Each fielder, other than the first baseman or catcher, may use or wear a leather glove. The measurements covering size of glove shall be made by measuring front side or ball receiving side of glove. The tool or measuring tape shall be placed to contact the surface or feature of item being measured and follow all contours in the process. The glove shall not measure more than 12" from the tip of any one of the 4 fingers, through the ball pocket to the bottom edge or heel of glove. The glove shall not measure more than 7¾" wide, measured from the inside seam at base of first finger, along base of other fingers, to the outside edge of little finger edge of glove. The space or area between the thumb and first finger, called crotch, may be filled with leather webbing or back stop. The webbing may be constructed of two plies of standard leather to close the crotch area entirely, or it may be constructed of a series of tunnels made of leather, or a series of panels of leather, or of lacing leather thongs. The webbing may not be constructed of wound or wrapped lacing to make a net type of trap. When webbing is made to cover entire crotch area, the webbing can be constructed so as to be flexible. When constructed of a series of sections, they must be joined together. These sections may not be so constructed to allow depression to be developed by curvatures in the section sides. The webbing shall be made to control the size of the crotch opening. The crotch opening shall measure not more than 4½" at the top, not more than 5¾" deep, and shall be 3½" wide at its bottom. The opening of crotch shall not be more than 4½" at any point below its top. The webbing shall be secured at each side, and at top and bottom of crotch. The attachment is to be made with leather lacing, these connections to be secured. If they stretch or become loose, they shall be adjusted to their proper condition. The glove can be of any weight. See Diagram No. 4.

DISCUSSION

All gloves must be made of leather (see Rule 1.12; Rule 1.13; and Rule 1.14). Unlike the baseball, which must be made out of cow hide or horse hide [Rule 1.09], the rules do not specify a type of leather.

Illegal glove [Rule 1.14]

http://mlb.mlb.com/video/play.jsp?content_id=18145673&topic_id=9780550&c_id=mlb

There is no penalty for a catch made with an illegal glove. [BRD]
A catch made with an illegal glove is a legal catch. [PBUC] Get rid of the glove and keep the play.

Note that the OBR does not require any defensive player to wear a glove.
A fielder's glove must comply with the dimensions addressed in Rule 1.14, therefore most catcher mitts and first baseman gloves will not comply and are illegal.

HISTORY
In 1990 MLB placed a renewed emphasis on reigning in illegal gloves.
http://articles.latimes.com/1990-05-02/sports/sp-56_1_12-inch-gloves
http://www.deseretnews.com/article/94262/BASEBALL-CRACKING-DOWN-ON-GIANT-GLOVES.html