Is a Turnover Hangover the Biggest Threat to Prosperity in 2014?
Annually, Phil Steele tries to winnow down the list of teams who could be considered contenders for a national championship by looking at the statistical profile of past participants in the title game the season before they got to the big game. If a team doesn't measure up to the minimum standard in each statistical category, then they are eliminated. Perhaps not surprisingly, Nebraska was eliminated on the basis of its turnover margin in 2013. Turnovers have been a concern in almost every season under head coach Bo Pelini, so to suggest there's a carryover does not seem far fetched. Using Nebraska's stats since 1993 reveals a few things.
Statistics from 1993 onwards were used but there was a slight change within that data set. Bowl games were not included in final statistics prior to 2002. There are some interesting findings:
The regular season turnover margin was positive in every season from 1993-2001. That's a span where Nebraska played for five national championships and missed on playing for a couple more by just a hair. Some of the best seasons Nebraska had in terms of wins were just 1 to 3 turnovers in positive territory though with the best in that span at +13 in 1995.
The 2003 season is a huge outlier. This becomes important later, but Nebraska was at +23 that year (where the team went 10-3) after being -3 the year before (a 7-7 season) and -12 the year after (5-6). Mathematically, this really undermines the idea of carryover from one year to the next, though those numbers were amassed with three different defensive coordinators.
Bill Callahan's teams never had a season with a positive turnover margin. There have been all kinds of reasons offered for why things fell apart for Callahan, but on the field turnovers played a huge role. The -17 margin in 2007 was ultimately his undoing and the worst for Nebraska in the two decades examined.
Bo Pelini's only had one season with a positive turnover margin. That was the 2009 season and it was the one where his season ending remark, "Nebraska's back and we're here to stay" rang true.
The turnover margin in one season was a poor predictor of the margin in the next season. Beyond the previously mentioned outlier, even if you look at just 2004 onward there's basically zero variance explained by the prior season's number.
The direction of the turnover margin was a much better predictor of next season's direction. If you ignore the number of turnovers and just give assign a +1 for a positive margin, a -1 for a negative margin and a zero for the one season (2006) that was even, we can explain 18% of the variance in the direction of the turnover margin if we know what happened the year before. This is probably the product of how streaky Nebraska's been in this department with a lot of consecutive years in positive territory and a lot of consecutive years in negative territory.
The turnover margin is a good predictor of the winning percentage in the same season. A third of the variance in winning percentage could be explained simply by knowing the turnover margin. Some of the bigger outliers in this department came under Pelini where the team was -11 in 2008 but still won 9 games and was -12 in 2012 and still won 10.
The direction of the turnover margin is an even better predictor in the same season. Well over half (nearly 59% of the variance) in win percentage over that span could be explained by whether a team had a positive, neutral, or negative turnover margin that year.
The results both agree with Phil Steele and disagree. Given that Nebraska had a negative turnover margin a year ago, that appears to be the likeliest outcome for this season as well. From what Tommy Armstrong has shown on the field, that could be an understatement. However, the -9 number that Ohio State had in 2005 wouldn't seem all that different from Nebraska's -11 a year ago, based on this admittedly limited analysis. In other words, you probably wouldn't change your opinion of NU's prospects for this season if Armstrong had managed to avoid throwing 2 of the interceptions he had at Purdue.
Assuming that Nebraska would have to win their conference in order to play for the national championship, a positive turnover margin would seem like a prerequisite for winning the Big Ten as well. Every time that NU won their conference in the 1990's, they did it by getting more turnovers from their defense than the offense surrendered. The near miss in 2009 was the last team to stay in positive territory. Bill Callahan's one team that wasn't negative in turnover margin played in the conference championship game.
It might not be fair to say that everything is riding on turnover margin for the Huskers, but it's clearly important. Florida State finished third nationally in the category on their way to a title last season. The Huskers would do well to follow their example.