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.
Penalty (gridiron football)
Moreover, the game clock will run once the ball is placed. If such a runoff occurs with 10 seconds or less remaining, the half automatically ends. Since the enforcement of the 10-second runoff, eight regular season NFL games ended automatically due to this rule: 2005 Arizona-St. Louis, 2009 Cincinnati-Green Bay, 2011 Chicago-Oakland, 2012 Washington-Philadelphia, 2012 New England-Arizona (which cost New England the chance to attempt a field goal at the end of the half in a game they eventually lost by two points), 2014 St. Louis-Tampa Bay (which cost Tampa Bay a chance to attempt a game-winning field goal), 2015 New England-New York Jets (which cost the Jets an attempt to throw a Hail Mary and force the game to overtime) and 2017 Atlanta-Detroit (which cost the Lions a chance to win the game). A pre-season game in 2006 between Houston and Kansas City had the first half end automatically due to an intentional grounding foul with less than 10 seconds left. A 2013 divisional playoff game between the New Orleans Saints and the Seattle Seahawks also ended on a 10-second runoff after Saints wide receiver Marques Colston threw an illegal forward pass.