NFHS Rule 4-2
Article 1 … All players on a team shall wear:
a. Like-colored uniforms consisting of shirts and shorts, pants or skirts, in one or two pieces, with the exception of the libero whose uniform shall meet the requirements of 4-2-2;
b. Uniforms that are free of hard and unyielding items (buttons, zippers, snaps, fasteners, etc.);
c. Uniforms that also may include compression shorts which are unadorned and of a single color similar to the predominant color of the uniform bottom;
d. Uniforms as intended by the manufacturer, and have the following restrictions:
1. Bare midriff tops are not allowed.
2. The uniform top must hang below or be tucked into the waistband of the uniform bottom when the player is standing upright.
e. Uniforms in the playing area. Removal of any part of the uniform is unacceptable behavior.
Article 2 … The libero must wear a uniform top that is immediately recognized from all angles as being in clear contrast to and distinct from the other members of the team. The primary color of the libero’s uniform top must be different from any color that appears on more than 25 percent of the body of teammates’ uniform top. In determining the body of the uniforms, the sleeves and collar should be ignored. The libero uniform must have a legal number. The style and trim of the libero’s uniform top may differ from teammates’ uniforms, but the shorts must be like-colored to teammates.
Article 3 … Each player, including the libero, shall be identified by a number on the uniform top which is not a duplicate of a teammate’s number.
Article 4 … The number shall be:
a. Permanent and clearly visible;
b. Not more than two digits;
c. A plain, Arabic numeral of solid color, where either the body of the number (measuring not less than ¾ inch in width at its narrowest point) or the surrounding solid color(s) of trim (a contrasting border not to exceed ½ inch in width at its widest point) is a color that is in sharp contrast to the color of the uniform top. A shadow on part of the number not to exceed ½ inch at its widest point is permitted but shall not be used to make the number clearly visible regardless of the color;
d. Located in the upper front and back of the uniform top;
e. At least 4 inches tall on the front of the top and at least 6 inches tall on the back of the top;
f. Placed so the top of the number on the front of the uniform is no more than 5 inches down from the shoulder seam; or placed so the number is centered no more than 5 inches below the bottom edge of any neckline ribbing, placket or seams on the uniform top.
Article 5 … If a visible number is worn on the uniform bottom, it shall be the same number as on the uniform top.
Article 6 … Appropriate playing shoes shall be worn.
Article 7 … If undergarments such as t-shirts, body suits, etc., are worn in such a manner that they are exposed, they shall be of a single color similar to the predominant color of the uniform top.
Article 8 … Players shall not wear undergarments or tights which extend below the uniform bottom.
Article 9 … A single partial/whole manufacturer’s logo/trademark/reference, no more than 2 ¼ square inches with no dimension more than 2 ¼ inches, is permitted on each piece of the uniform provided placement does not interfere with the visibility of the player’s number.
Article 10 … An American flag, not to exceed 2 by 3 inches, and either a commemorative or memorial patch, not to exceed 4 square inches and with Association approval, may be worn on each item of the uniform apparel provided neither the flag nor the patch interferes with the visibility of the player’s number.