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Alabama By the Numbers: Turnover Margin

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The common metric to measure turnovers in college football is ye olde Turnover Margin. Count up how many fumbles and interceptions your team made, subtract the ones you lost and divide by games played and VOILA! Statistical goodness!

Obviously, there are a number of issues with the data and even more problems with how it's usually interpreted. But, overall, it's a pretty good starting point for looking at how a team performed in terms of limiting unwanted changes of possessions on their part and encouraging the opposite for the opponents.

Here is Alabama's turnover margin over Coach Saban's tenure in Tuscaloosa (the ordinal numbers indicate the Crimson Tide's ranking nationally):

Alabama Turnover Margin (per game) 2007-2011


For 2007 and 2008, the good news was that Alabama's turnover margin was well in the positive. The bad news was that it was struggling to remain in the top third in the country. That changed dramatically during the Crimson Tide's 2009 National Championship run when the turnover margin shot up to fourth in the nation. Pundits promptly predicted a fall from the heights for the following season and sure enough, Alabama's turnover margin fell... a whopping ten spots.

Then, weirdly enough, it fell again as the Crimson Tide rolled to another National Championship last year. So let's look a little closer at the numbers to see what happened. Here are the total number of turnovers for each of the past five seasons (for all the following charts, keep in mind Alabama played an extra game in the 2008 and 2009 seasons).

Alabama Total Turnovers 2007-2011


And, yes, Alabama did sustain a healthy dip in turnovers gained last year -- 23% less to be exact. Yet, while the 20 turnovers was the least for the Crimson Tide to collect over the past half-decade, Alabama's opponents were enduring a scarcity of possession-changing events as well. The even dozen turnovers lost to opposing squads in 2009 and 2011 is probably not a coincidence.

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But let's break this down a bit further, shall we? Here are the total number of interceptions Alabama gained and lost over the last five seasons:

Alabama Interceptions 2007-2011


This shows pretty much exactly where Alabama's incredibly strong turnover margin emerged from in 2009 and 2010 -- a defensive secondary reeling in a metric ton of interceptions while the offense refused to return the favor. Things seem to have reversed in 2011 but... Hey! Waitamint? Didn't Alabama have the best passing defense in the country last year? Why, yes they did. Perhaps there is more at work here than meets the eye.

But on to fumbles. Like the two charts above, this graph charts the total Alabama gained and lost since 2007:

Alabama Fumbles 2007-2011


This enigmatic looking glyph is pretty much the epitome of "small sample size." Yet the trend suggested here seems reasonable enough. In 2010 Alabama lost significantly more fumbles than they gained while last season marked the first time in the past five years the Tide picked up more drops than they put on the ground themselves. Clear as mud, right?

While the raw turnover numbers give a general idea of things it's pretty obvious that there's a lot of information we're missing in trying to figure out how good (or bad) Alabama did in terms of fumbles and interceptions last season. So, tomorrow, we'll start delving a bit deeper into the numbers.