In the chart below, the black dots are the yards/possession per game, the gray dots are the average yards/possession allowed for each opponent for the season, the green bars are the difference between the black and gray, and the red line is Kansas State's average yards/possession for the season. The conclusion is fairly obvious. For the first half of the season, Kansas State had the nation's most effective offense. Combined with good field position and a low turnover rate, they had the nation's highest scoring offense by points/possession. Over the last four games Kansas State was not only less good, they were significantly worse than each opponent's average opponent.
What happened? The short answer is that Collin Klein got knocked on the noggin against Oklahoma State. Klein still finished the season as a top 5 quarterback in EPA+/pass, but his opponent-adjusted production fell 35% between the first 9 and last 4 games by expected points added per pass. Before Oklahoma State he was the nation's most efficient passer and, had he stayed on his first half pace, he would have finished the season in a virtual tie with Baylor's Nick Florence for the nation's top spot. Production per rush also fell in the last four games, but not as far and from a much lower starting point.
And this brings us to the great Kansas State myth. The perception among most is that Kansas State won with good defense, no mistakes, a solid running game, and then Klein made the necessary plays to put them over the top. Nothing could be further from the truth (almost). Few teams allowed more plays/possession and 76 teams allowed fewer yards/possession than Kansas State. The defense wasn't great, but they took advantage of good field position and prevented explosive plays fairly well (but were well short of elite), so teams were forced to move the ball down the field one play at a time. They were top 30 in turnovers forced per play but were 2nd nationally in turnovers per possession. As a result, the defense was able to return the favor of good field position to the offense (best in the country) despite allowing 33 yards per possession and finishing 39th in points/possession.
Kansas State ran the ball more than 60% of the time, but not because the running game was good. They were 73rd in opponent-adjusted yards per rush and 60th in explosive plays per rush; they were much better by EPA+/rush only because Klein was a conversion machine. The passing game, on the other hand, was top 10. They averaged only 35 yards/possession, but with good average starting field position that was enough to reach the red zone on 46% of possessions. The only part of the Kansas State myth that was really true is that they rarely turned over the ball (before Klein got bonked, at least).
Like Boise State, I don't assume regression in turnovers for Kansas State. It is a skill these programs have mastered. But I do project regression offensively when they lose a Heisman caliber talent at quarterback. Remember, Kansas State was elite in only two areas in 2012. They threw the ball well and won the turnover battle. This resulted in good field position and allowed them to scored points while running 60% of the time. Without the field position, the defense allows more points and forces fewer turnovers, which then translates into worse field position for the offense, which leads to fewer points and more turnovers. Kansas State is forced to be more aggressive on offense and the game speeds up, playing right into the hands of the Baylors, West Virginias, and Techs of the world. Things unravel quickly. Assuming Kansas State gets post-noggin-bonking level play at quarterback in 2013, Kansas State could still be a solid team, but they will slip back into a muddy Big 12 pack.