A system of assignment of jersey numbers was initiated in American football's NFL in 1952; it was updated and made more rigid in 1973, and has been modified slightly since then. Numbers are always worn on the front and back of a player's jersey, and so-called "TV numbers" are worn on the sleeve or shoulder. The Cincinnati Bengals were the last NFL team to wear jerseys without TV numbers on a regular basis in 1980, though since then several NFL teams have worn throwback uniforms without them, as their jersey designs predated the introduction of TV numbers. In 2007, the Cleveland Browns, Philadelphia Eagles, and Pittsburgh Steelers wore throwback jerseys without TV numbers. Players' last names, however, are required on all uniforms, even throwbacks which predate the last name rule. Since 2008, TV numbers have not been mandatory under NFL rules. Some uniforms also feature numbers either on the front, back, or sides of the helmet (in pro football, these were most prominently worn on the San Diego Chargers "powder-blue" uniforms). Players have often asked the NFL for an exception to the numbering rule. In 2006, for example, New Orleans Saints running back Reggie Bush requested to keep the number 5 he wore in college. His request was declined, and he was assigned number 25 by the team. Below is the numbering system established by the NFL, and in place since 1973:
- Numbers 1 to 19 are worn by quarterbacks, kickers, and punters. Since 2004, wide receivers are also allowed to wear numbers between 10 and 19 if they so choose, even if there is an 80-89 number available. In the rare event that all numbers from 10-19 and 80-89 are taken, receivers are allowed to wear single digit numbers, such as Biren Ealy, current NFL Free Agent, on the Baltimore Ravens then wore a single digit number in the 2009 Preseason.
- Numbers 20 to 49 are worn by running backs, tight ends (who may wear a number between 40-49 when 80-89 are unavailable), cornerbacks and safeties.
- Numbers 50 to 59 are worn by linebackers and centers.
- Numbers 60 to 79 are worn by tackles, guards and defensive linemen (the defensive ends, defensive tackles or nose guard).
- Numbers 80 to 89 are worn by wide receivers and tight ends.
- Numbers 90 to 99 are worn by linebackers and defensive linemen. In use since 1984.
- Numbers 0 and 00 are no longer used, though they were issued in the NFL before the number standardization in 1973. George Plimpton wore 0 during a brief preseason stint at quarterback for the Detroit Lions. Jim Otto ("aught-oh") wore number "00" during most of his career with the Oakland Raiders. Wide receiver Ken Burrough of the Houston Oilers also wore "00" during his NFL career in the 1970s.
This NFL numbering system is based on a player's primary position. Any player wearing any number may play at any position at any time (though players wearing numbers 50-79 must let the referee know that they are playing out of position by reporting as an "ineligible number in an eligible position"). It is not uncommon for running backs to line up at wide receiver on certain plays, or to have a lineman or linebacker play at fullback or tight end in short yardage situations. In preseason games, when teams have expanded rosters, players may wear numbers that are outside of the above rules. When the final 53-player roster is established, they are reissued numbers within the above guidelines. This numbering system originated in football's past when all teams were using some variation of the single wing formation on offense. When teams switched to the T-formation in the 1930s and 40s, the numbers were taken with them to whatever position evolved from the old single wing position. The system was first used in college football and was used only informally in the NFL until 1952; under the original, somewhat informal system, the backs were numbered 1-4, and the line 5-8. Tailbacks or left halfbacks therefore had a number in the 10s. The blocking back, which evolved into the quarterback in the T formation, had a number in the 20s. The fullback had a number in the 30s and the right halfback had a number in the 40s. On the offensive line, the center was in the 50s, the guards were in the 60s, the tackles were in the 70s and the ends were in the 80s. In earlier times, defensive players would wear a number that reflected their offensive position, as many players played both offense and defense. For example, quarterbacks and halfback would usually play in the defensive backfield and so had numbers in the 10s, 20s and 40s. Fullbacks were often linebackers and had numbers in the 30s; Centers and guards were linebackers as well and had numbers in the 50s and 60s respectively. Guards and tackles played the defensive guard and tackle positions and had numbers in the 60s and 70s respectively. Ends had numbers in the 80s - split ends would be cornerbacks and tight ends would be defensive ends. The All-America Football Conference (AAFC) had a different numbering system with quarterbacks in the 60s, fullbacks in the 70s, halfbacks in the 80s, ends in the 50s, tackles in the 40s, guards in the 30s and centers in the 20s. When the AAFC merged with the NFL in 1950, the AAFC players kept their old uniform numbers which caused confusion and resulted in the NFL moving to a standard numbering system in 1952. This resulted in many established players having to change their numbers in mid-career. Most notably, Cleveland Browns quarterback Otto Graham had to switch from number 60 to number 14. Though the Hall of Famer was more well-known with number 60, the Browns ironically retired the number 14 in his honor while number 60 remains in circulation. His fellow Hall of Fame teammate, Lou Groza, was allowed to keep number 76 (also retired by the Browns) despite playing kicker until his retirement in 1967 since he was also an offensive tackle.