The digit 7 is not illegal or banned under standard international FIBA rules or within professional leagues like the NBA and WNBA, where players are fully permitted to select single-digit numbers ranging from zero to nine. However, traditional American high school and collegiate rulebooks governed by organizations like the National Federation of State High School Associations and the NCAA historically restricted jersey digit choices to numbers utilizing digits zero through five. This regulation was originally implemented because it allowed basketball referees to clearly signal player fouls to the official scorer's table using one hand, which became physically impossible when attempting to show higher digits like 6, 7, 8, or 9 using standard hand-signaling conventions. Consequently, players across scholastic and amateur American divisions could not wear those specific numbers, though modern rule changes and professional leagues have since eliminated these legacy restrictions.