 The runback is the most rare of the conversion rules, and is most often implemented in one-on-one games.In this version, the play does not end once the ball crosses the goal line; instead, the player with the ball must change direction and advance it all the way back to the other end zone for two points.The game ends when a pre-determined number of touchdowns or points has been scored, or an arbitrary time is reached (for instance, dusk or the start of school).