<P> In American high school football (in most states), the play is over once the ball becomes dead or the defense takes possession . In many other levels of football, including the CFL, NFL, and American college football, the play continues after a turnover to the defense . This allows the defense to return the ball to the opponent's end zone for two points and also allows for a one - point safety . Two states, Texas and Massachusetts, play high school football under NCAA rules and thus allow the defense to score on an extra-point attempt . </P> <P> In American high school and college football, the line of scrimmage is the three - yard line . </P> <P> In American football, the game clock does not run during an extra-point attempt, except for some rare circumstances at the high - school level (some state associations allow for the clock to run continuously in the second half if one team is leading the other by a large margin) and for arena football, which runs the clock continuously except during the final minute of each half and overtime . In Canadian football, the clock runs during a conversion attempt except during the last three minutes of each half . </P> <P> Prior to the 2015 season, the NFL used the two - yard line for all conversion (P.A.T.) attempts . In Canadian football, the line of scrimmage was from the five - yard line . </P>

When was the extra point added to college football