or the quarterback could make an impromptu run on his own (called a "scramble") to avoid being sacked by the defense. Depending on the offensive scheme used by their team, the quarterback's role can vary. In systems like the triple option, the quarterback will only pass the ball a few times per game, if at all, while the pass-heavy spread offense, as run by schools like Texas Tech, requires quarterbacks to throw the ball on most plays. The passing game is emphasized heavily in the Canadian Football League (CFL), where there are only three downs (as opposed to the four downs used in American football), a larger field of play and an extra eligible receiver. Different skillsets are required of the quarterback depending upon the offensive system. Quarterbacks that perform well in a pass-heavy spread offense system, a popular offensive scheme in the NCAA and NFHS, rarely perform well in the National Football League (NFL), as the fundamentals of the pro-style offense used in the NFL are very different from those in the spread system, while quarterbacks in Canadian football need to be able to throw the ball often and accurately. In general, quarterbacks need to have physical skills such as arm strength, mobility and a quick throwing motion, in addition to intangibles such as competitiveness, leadership, intelligence and downfield vision. In the NFL, quarterbacks are required to wear a uniform number between 1 and 19. In the National Collegiate Athletic Association (NCAA) and National Federation of State High School Associations (NFHS), quarterbacks are required to wear a uniform number between 1 and 49; in the NFHS, the quarterback can also wear a number between 80 and 89. In the CFL, the quarterback can wear any number from 0 to 49 and 70 to 99. Because of their numbering, quarterbacks are eligible receivers in the NCAA, NFHS and CFL; in the NFL, quarterbacks are eligible receivers if they are not lined up directly under center. Leadership Often compared to captains of other team sports, before the implementation of NFL team captains in 2007, the starting quarterback is usually the de facto team leader and a well-respected player on and off the field. Since 2007, when the NFL allowed teams to designate several captains to serve as on-field leaders, the starting quarterback has usually been one of the team captains as the leader of the team's offense. In the NFL, while