MLB Uniform Rules & Regulations

Shirt & Jersey Rules:

• All players must wear their uniform numbers on the back of the uniform.
• Jerseys may not be so baggy as to, or otherwise sized in a manner which may, interfere with umpires' ability to make calls.
• Jerseys may not intentionally be untucked.
• Under no circumstances may a jersey be ordered at or altered to a length where it cannot properly be tucked in.
• When any portion of a Player's undershirt is visible, the Player may only wear an undershirt that is in the Club's primary color or the heather gray color supplied by the Club.
• No corporate identification or other logos of any kind are to be visible on any part of the undershirt, except for any Club logo or Major League Baseball silhouetted batter logo.
• A pitcher may wear a jacket while a baserunner. If worn (on the bases), the jacket must be buttoned.
• A pitcher may not wear a jacket while batting.
• No other player is permitted to wear a jacket while a baserunner, a batter, a defensive player, or a coach on the baselines.