Comparison of American football and rugby union
A rugby union game is divided into two halves of 40 minutes (or shorter for lower-grade games, and breaks given halfway through each half if playing conditions are considered to be extreme) separated by a half time period of up to 15 minutes in an international match. Most notably, a rugby union game will continue after the scheduled end of a half (half-time or full-time) until the ball becomes dead - any occurrence that would have play restart with a scrum or lineout, or when a team scores. This has led to some "nail-biting" finishes where teams losing by only a small margin work their way towards scoring, and games can go on several minutes over time. Something similar can occur at the end of either half in American football, though usually for only a few seconds of additional time, because a play that begins before the half expires continues until the ball is dead regardless of whether there is any time left on the clock. In both sports, the clock is also stopped during substitutions and for injuries, so the referee does not need to add stoppage time as is done in soccer/Association football. American football games are made up of four quarters of 15 minutes each (less at the high school and youth levels), but the clock stops and starts according to specific rules, so that a 15-minute quarter lasts much longer.
Official (American football)
Because their regular season spans only 17 weeks, the NFL is one of only two major sports leagues in the United States that only pay their officials on a contract basis as opposed to being full-time salaried employees, the other being Major League Soccer. Advantages to this system include being able to eliminate unqualified officials simply by not offering them a contract the following season, where terminating full-time employees would require them to show cause. Critics argue that full-time officials would be free from the distractions of a second job, but proponents of part-time officials point out that the NFL would lose a number of qualified officials because many of them are owners, presidents, or CEOs of various companies. Proponents also argue that there is only one game per week and the regular season is only four months long, and that having full-time officials does not necessarily guarantee that they will make fewer officiating mistakes. The level of training and review in which NFL officials participate makes additional time redundant. In any event, veteran officials can earn substantial salaries for their work. The NFL Referees Association serves as the union that represents officials in the NFL.