Why didn't Oklahoma attempt an extra point after their fumble recovery touchdown on the last play of regulation time in its 12/7/13 NCAA game vs Oklahoma State? Is there a NCAA rule answering this question?
NCAA Football Rule 8-2-3-a, covering the "try" (either extra point or two-point conversion), states:
a. The ball shall be put in play by the team that scored a six-point touchdown. If a touchdown is scored during a down in which time in the fourth period expires, the try shall not be attempted unless the point(s) would affect the outcome of the game.
If the score had been 34-32 or 33-32 in favor of Oklahoma State or tied 33-33 after the touchdown, then Oklahoma would have attempted the try. But since Oklahoma already had the lead, it was not necessary.
My interpretation of "unless the point(s) would affect the outcome of the game" leads me to believe that the try is only attempted if it would help the scoring team; i.e. a team that scores to take a one-point lead as time expires would not have to attempt the try, even though the defense could in theory score two points on a turnover or blocked kick.
Note that the NFL's rules differ on this point; in the NFL, the try is always attempted except after touchdowns in sudden-death overtime.