practice for fear of teams running out of numbers; the rule book requires teams to make available retired numbers for new players should they exhaust all available numbers at a particular position. In the XFL, the NFL numbering conventions were followed with a slight exception being that wide-receivers are allowed to wear single-digit numbers (i.e. 1–9); the NFL itself added that allowance starting in 2021. NCAA According to NCAA rule book, Rule 1 Section 4 Article 1 "strongly recommends" numbering as follows for offensive players: Back 0–49 Center 50–59 Guard 60–69 Tackle 70–79 End 80–99 Otherwise all players can be numbered 1–99; the NCAA makes no stipulation on defensive players. Two players may also share the same number, although they may not play during the same down. Starting in the 2020 NCAA football season, the use of duplicate numbers will be restricted to only two players on a team, and players will be allowed to wear No. 0. Two players, both placekickers, have worn No. 100 in NCAA history. Both did so as part of centennial celebrations in the 1960s, with special dispensation from the NCAA: West Virginia's Chuck Kinder (not the writer of the same name), who did so in 1963 to commemorate the state of West Virginia's 100th anniversary, and Kansas' Bill Bell, who did so in 1969 to commemorate 100 years since the first organized college football contest. High school On high school and other lower youth teams, jerseys with different number ranges are different sizes, and since many of these teams do not reorder jerseys every year, players are often assigned numbers based more on jerseys that fit them rather than specific position. Permian High School (of Friday Night Lights fame) in Odessa, Texas plays in the one state which uses NCAA rules for high school football; yet Permian's tradition is that quarterbacks will wear numbers in the 20s unlike most schools in college or high school. Although previous editions of the National Federation of State High School Associations rule book indicated a recommended numbering system nearly identical to the NCAA's, later editions from approximately 2000 onward only indicate the bare minimum requirements: offensive linemen must be numbered from 50 to 79, while all other positions including backs and ends must wear numbers either from 0 to 49 or 80 to 99. The number 0 was made legal in 2022, although it remains banned as the